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Author Topic:   Mercury 90-HP FOURSTROKE: Carburetor Problems
DIRTBIKERICK posted 12-18-2005 03:03 PM ET (US)   Profile for DIRTBIKERICK   Send Email to DIRTBIKERICK  
Hi all, I am hoping for help. In July of this year I put all my hard-earned coin down on a new 170 Montauk with the Mercury 90-HP Saltwater FOURSTROKE carburetor motor, passing on the EFI version of the same engine. Total time now is 14-hours of use with three no-start's at the launch ramp and one half-hour no-start out on the kelp line. Now I find out [problems with the carburetors on Mercury FOURSTROKE motors] are a common and a recurring event, even after [the carburetors] have been cleaned out.

What do I do now?

The boat is at the dealer now with no answer yet. I am gun shy about future [problems] with these carburetors. When I took delivery of the boat even the mechanic then said he put a water separator in the [fuel system] because they have had problems with debris in jets.

Help, bummed out Rick

WT posted 12-18-2005 03:32 PM ET (US)     Profile for WT  Send Email to WT     
I use Mercury Quickleen in my 2004 Mercury 90 HP 4 stroke outboard.

jimh posted 12-18-2005 05:06 PM ET (US)     Profile for jimh  Send Email to jimh     
Often problems with starting an engine can be related to poor procedures being used. Every engine has a unique starting procedure that is required. Be sure you are using the proper procedures when starting. Your owner's manual should have a thorough explanation of how to start the engine.

Carburetors have been used on four-stroke engines for about about 100 years. They are a mature technology and are quite well suited for marine applications where the ambient air temperatures are generally moderate. I don't see any evidence that fuel injectors are less prone to clogging from debris in the fuel system than carburetors. In both devices the fuel must pass through restrictive orifices. If you have debris in your fuel system you need to be diligent about filtering the fuel.

Carburetors are prone to problems if they sit for long periods of non-use and the fuel inside them evaporates. It can occur that residue from evaporated fuel will cause problems. However, there are millions of engines with carburetors which start and run smoothly. If your fuel system has debris you will have to remove it. If your carburetors are clogged with fuel residue, you will have to clean them. The position in which the engine is stored when not running can also affect the carburetors. It is not unusual for fuel to drain from the carburetor float-bowls if the engine is tilted to a horizontal position in storage. Carburetors without fuel will make for very difficult starting. On an engine in good tune, with fuel properly primed, and spark plugs in good condition, starting should occur after just two or three rotations of the crankshaft. If your engine is not starting like that there is something wrong.


--take care in fueling with quality gasoline that is free of contaminants
--check all fuel filters, replace any with debris
--check the spark plugs for proper gap and to be free from fouling
--use fuel additives designed to prevent formation of gum and varnish deposits
--review with the manufacturer representative the proper procedures for starting the engine
--review any procedures need for shutting down the engine and storing it when not in use.

If the engine fails to start after following the recommended starting procedure, then you have a problem. It may be due to a defect in manufacturing of the engine. If you purchased the engine new there is a warranty in effect. An engine which fails to start is clearly not performing as intended, so you should seek a remedy with the manufacturer and his representatives. Insist they correct this problem. The engine manufacturer and his representatives may reasonably point out that if the problem was caused by contaminated fuel they are not liable to pay for repairs.

DIRTBIKERICK posted 12-18-2005 05:54 PM ET (US)     Profile for DIRTBIKERICK  Send Email to DIRTBIKERICK     
Thanks for your replies, this is a brand new 2005 boat/engine/trailer package assembled by Boston Whaler, 14-hours time. I am a automotive master mechanic, own a auto repair facility and am quite sharp when it comes to diagnosing fuel and ignition systems. It is the absence of fuel that is my poor running problems. If the boat sits and is not started for three weeks or so it takes a long time to finally hit on all cylinders. I can introduce propane with a snorkle thru the air intake and it cleans out and runs smooth, thus absence of fuel thru idle circuit. I was told to leave the engine vertical and not run the carburetors empty like the old days. Cold enrichment, (start up) is done with the carburetor's built in enrichment system, normal fuel scale should not plug jets or passages in that short of time. My guess is California emissions engines run so lean, (I call it welfare) that they're plugging up the small idle jets. EFI systems are under pressure 35-PSI appproximately, and vacuum is drawing fuel thru jets at a low Hg [vacuum pressure]. The bottom line for me is a new, high-dollar, high-tech motor should not have problems like this without outside influence entering the fuel system. I know today's fuels go bad quick but not in three weeks. Thanks, rick
LHG posted 12-18-2005 07:01 PM ET (US)     Profile for LHG    
My Mercury mechanics have told me these Mercaha carburetor 90-HP four-stroke motors have had continuing carburetor clog-up problems, because of the miniscule passages in them, much smaller than the old carburtors two-strokes used. They are also a Yamaha dealership. Since Mercury was getting these engines from Yamaha, their hands were tied, and they had to wait for Yamaha to get out the EFI versions.

Their opinion is the only four-stroke to own is an EFI, which doesn't foul up. For those that have the carburetor version, the advice from them, at least, is to run Sta-Bil continuously in the engines, and definitely when you are not going to use it for a week. It prevents these tiny passages from getting gummed up.

Dick posted 12-18-2005 07:16 PM ET (US)     Profile for Dick  Send Email to Dick     
I had the same problem with my 1999 Merc carburetor 50-HP four-stroke, Yamaha powerhead. Running StaBil eliminated it.
elaelap posted 12-18-2005 07:37 PM ET (US)     Profile for elaelap  Send Email to elaelap     
I put 370 hours on a 2002 Yamaha 50-HP carburetor four-stroke High Thrust motor in little more than a year, and the boat/motor's current owner, CW member Steve/17 Bodega, has put even more hours than that on the motor over the past almost two years. Neither of us had any problems whatsoever. I can't speak for Steve, but when I owned the motor it never once failed to start immediately with the first turn of the key. I never used additives in the gasoline (Shell 89 octane). I'm not sure that recent Yamaha and Mercury powerheads are identical; if they are, I've sure been lucky compared with some Mercury owners who've commented at this website.


jimh posted 12-18-2005 07:39 PM ET (US)     Profile for jimh  Send Email to jimh     
I infer you are in California. Perhaps your local blend of gasoline is not compatible with that engine. It may be loaded with alcohol or other oxygenates. Are outboards manufactured with special emissions settings for sale in California? I was under the impression all outboards got the same fuel settings nationwide.

If a can of StaBil or other fuel conditioner gets rid of the problem, that sounds like the easiest fix. Or perhaps larger jets, but it is likely illegal to tamper with those settings because of EPA regulations, particularly in California. It's too bad, as most of the time these new lo-emission engines run quite a bit better than a classic two-stroke. Sounds like this one is not quite on that path yet.

Chuck Tribolet posted 12-18-2005 09:03 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
My buddy Kawika has a carbed Merc 4-stroke on his Montauk 170,
and the only time he's had starting problems it was a fried
starter motor. His does get used every weekend.


DIRTBIKERICK posted 12-18-2005 10:02 PM ET (US)     Profile for DIRTBIKERICK  Send Email to DIRTBIKERICK     
Thanks again for your responses, I tryed StaBil since my first poor running [problems] and have used that with each fuel up. My opinion is that until Mercury comes up with a real fix I am gonna have this problem over and over. I am not trying to be negative, but until there is an EFI motor on this boat--which I did not buy because the salesman said the carburetor version had no [problems]--I am going to be a unhappy camper. I even called back when the motor had three hours on it and tryed to get the EFI motor, offering to pay the extra $1,800. With a positive word, I love the 170, it is great handling, fast and stable, lots of working room. I also have an Air Warrior Centurion with the EFI 5.7. What a rocket and no running [problems] since new. Could I put outriggers on my wakeboard tower? Thanks, Rick
jimh posted 12-19-2005 10:15 AM ET (US)     Profile for jimh  Send Email to jimh     
The anecdotal evidence is that there are no problems with the Yamaha 90-HP four-stroke motor with carburetors, but there are definite problems with the Mercury 90-HP with carburetors, even though the power head components are believed to be the same. This raises the question, "Are the carburetors the same?"

We can get to the bottom of the carburetor problem fairly easily. Steve--take the cowling off of your Yamaha 90-HP four-stroke outboard and inspect the carburetors for some identifying name or number. Rick--you do the same with your Mercury motor. Maybe you can both take a digital image of the carburetors and we can compare them. It will be interesting to see if they are the same carburetors on both motors.

Rick--I'd keep taking that motor back to the dealer until they make it run properly. You bought a new motor. It should start and run like a new motor.

swist posted 12-19-2005 01:27 PM ET (US)     Profile for swist  Send Email to swist     
What are the implications (other than cost) of running Stabil year around to keep the passages clear?

I always assumed something intended for stored fuel must have some negative affact on non-stored fuel, otherwise why wouldn't whatever the active ingredient in Stabil be put in all gasoline to begin with?

sosmerc posted 12-19-2005 06:54 PM ET (US)     Profile for sosmerc  Send Email to sosmerc     
I have been a regular user and advocate for Sta-bil for sometime. However, recently I discovered some granular, sand or rustlike material in the measuring side of an un-opened Stabil container. I have seen similar "debris" or deposits on and inside fuel filters that I am now wondering if maybe the Stabil caused these deposits due to some kind of "fall-out". It concerned me enough that I have now switched to StarTron's fuel treatment to see how it does. StarTron supplies an interesting "poop-sheet" with their product that looks interesting.
Anyone else out there have any experiece with the StarTron product? (or similar experience with Sta-Bil?)
sosmerc posted 12-19-2005 06:56 PM ET (US)     Profile for sosmerc  Send Email to sosmerc     
Here's a link to some StarTron info.

jimh posted 12-19-2005 07:16 PM ET (US)     Profile for jimh  Send Email to jimh     
I think the carburetors on the Yamaha motor are made by Mikuni. Does that sound right to you Yamaha 90-HP owners? Look under your cowling and see what is there.

Here is what the carburetors looked like on a 2004 Mercury 90-HP four-stroke:

That silver gizmo on the front which is feeding the fuel to the carburetors has the name Mikuni molded on the cover. I assume it is the fuel pump. The name Mercury is molded into a lot of the covers on this engine, but this is the power head shipped over from Nippon which was the subject of the big legal action between Mercury and Yamaha last year (where Mercury has to go to court to force Yamaha to continue to sell them at the contract price through 2006).

RICK: Is this what your Mercury 90-HP four-stroke looks like?

How about you Yamaha owners. Does your 90-HP four-stroke look the same?

P.S. I took that picture at a Whaler dealer; it was a customer's boat in for service. This was in the spring of 2004. Looks like they were doing some engine work. I wonder what the problem was?

sosmerc posted 12-19-2005 08:43 PM ET (US)     Profile for sosmerc  Send Email to sosmerc     
The round looking device is not a fuel pump. It is a diaphragm assembly that pumps air into the carburetor under acceleration and this air is used to force additional fuel up the main nozzle to prevent stalling during rapid acceleration. It is also designed to act as a "coasting enrichener" during quick deceleration, to prevent stalling. The fuel pump is located at the back of the engine, just above the fuel filter in the picture.

This engine has two electro-thermal valves as part of a "PrimeStart" system (the white assemblies on the top of carburetor 1 and carburetor 3). These valves have a needle assembly that controls fuel flow into the venturi based on temperature. Electrical current flowing through the valves heats up wax inside that in turn moves the adjustment needles which eventually reduces or "leans" the mixture as the engine warms up.

Since the engine does have basically an "accelerator pump" you could try rapidly pumping the throttle prior to starting to see if this helps your starting problem. This procedure works well on some small four-strokes that are hard to start when cold.

I have worked on the Mercury 50-HP carburetor four-strokes (very similar carb setup) and I do know that carburetor sync and link is critical. And a good carburetor balancing tool is essential if the linkage has been "disturbed".

My guess is the Mercury shown here has the exact same carbs and linkage as the Yamaha version, though I do not know that as a fact.

That vacuum dashpot device does depend on several check valves for proper operation and I can see where that might cause some real problems if a check valve gets stuck open or closed.

jimh posted 12-19-2005 11:20 PM ET (US)     Profile for jimh  Send Email to jimh     
Thanks for the information. It sounds complex!
DIRTBIKERICK posted 12-20-2005 01:04 AM ET (US)     Profile for DIRTBIKERICK  Send Email to DIRTBIKERICK     
Thanks for all your help. Jim the picture of the Mercury is the same as mine. I can't take any pictures to compare because the boat is at the dealer, but I do remember Mikuni on the sides of the carbs. I will call the dealer tomorrow to check in, hope for good news. Rick
swist posted 12-20-2005 12:38 PM ET (US)     Profile for swist  Send Email to swist     
Still didn't get an answer on advisability of running Stabil all year. Perhaps no one knows?
sosmerc posted 12-20-2005 01:04 PM ET (US)     Profile for sosmerc  Send Email to sosmerc     
From what I have read, fuel conditioner is most effective if you put it in during fill-ups. It is of little value if your gas is already "old". So I would recommend using it year-round at the manufacturers recommended dosage. If it turns out your boating plans change and you don't get out in your boat for months, your fuel will always be ready!
jimh posted 12-20-2005 11:19 PM ET (US)     Profile for jimh  Send Email to jimh     
Also, we still need confirmation from owners of the Yamaha version of this engine. Does their engine use these same carburetors?
outragesteve posted 12-21-2005 02:33 AM ET (US)     Profile for outragesteve  Send Email to outragesteve     
I recently worked on a F100 Yami, and own a 22'Outrage w/ twin F100's. The engine I worked on would not start, and I thought at first it was electrical. I shot of starting fluid proved me wrong! I ended up taking off the carburetors, and re-building with kits from Yamaha. (Expensive!) I got the engine running, but it was not right. I borrowed a carburetor vacuum gauge tool, and set up the carburetors. It now starts very quickly, but runs rough on the top end. I've narrowed it down to one carburetor, because the low speed idle mixture screw has to be 5-6 turns out to run smoothly at an idle. What caused the problem was water in the fuel. I don't know if it was fresh or salt, but since the passages are so small in the carburetors, the water can sit and just block the flow of fuel. I've also been told it could be gas that's not "compatible" with these carbs. I'm now using StaBil in this boat and my own, and checking the water separators (Racor w/ bowls) every time I got out. Also topping off the tank at the end of the day. Good luck: getting the carburetors off is quite straight forward.
outragesteve posted 12-21-2005 02:36 AM ET (US)     Profile for outragesteve  Send Email to outragesteve     
By the way, the pic of the Merc carbs looks identical to the Yamaha carburetors. I'm going to order a Merc carburetor re-build kit and see how it compares to the Yamaha, just for fun!
jimh posted 12-21-2005 09:03 AM ET (US)     Profile for jimh  Send Email to jimh     
Steve--Thanks for the positive ID on the carburetors.

Your assessment that problems with starting and running could be related to water in the carburetor bowls is interesting. Another mechanic mentioned to me his experience in servicing a carburetor engine that had intermittent problems. The problem turned out to be small amounts of water which had made their way to the carburetor bowls. The water had separated from the gasoline and was trapped in the bowl, where the mechanic described it was "rolling around like a little marble." Draining the carburetor bowl was the only way to remove the water.

Chuck Tribolet posted 12-21-2005 10:50 AM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
FWIW, Mikuni is a Japanese carburetor manufacturer. My 240Z
had Mikuni-made SUs, and the racing Zs ran Mikuni-made Solexes. And I think I've seen Mikuni's on motorcycles.


Barney posted 12-21-2005 12:01 PM ET (US)     Profile for Barney  Send Email to Barney     
From my experience hard starting with that outboard was fixed like this:

Opened the Service manual to the Recommended Tests listed in the ignition section. [b]Number one[\b] on the list for "Engine Hard To Start Cold" was Debris in the carburetor enrichener circuit. Easy to work on with the manual. I blew out the upper enrichener and a wad of grit came out. Check the lower and put it back together. Fired right up.

One of the enrichener circuits was bone dry.


bobeson posted 12-21-2005 01:06 PM ET (US)     Profile for bobeson  Send Email to bobeson     

From my recollection of rebuilding my 2003 Merc 90hp 4stroke carbs earlier this year, the carbs are in fact Keihin brand, not Mikuni. I'll open up the cowling when I get home (if it's not raining tonight) and verify if people are still interested.

Having rebuilt multiple motorcycle carbs over the years, I was still surprised at the abundance of very small passages that had been gummed up in these particular carbs. I've never seen such a complex carb design as this one. I wish I had an EFI engine!

swist posted 12-21-2005 02:24 PM ET (US)     Profile for swist  Send Email to swist     
Well this is a little depressing. Bought a used 2004 Mtk 170 with that engine on it - very low hours - but unfortunately had to put it up for the Winter before I even got to take it out.

So here I am waiting until Spring to find out if I have a lemon for a motor..... I paid a lot of money out....

fishinchips posted 12-21-2005 05:15 PM ET (US)     Profile for fishinchips  Send Email to fishinchips     
I now always use Mercury quickleen.
Really does help ! No more problems.


bigjohn1 posted 12-21-2005 08:38 PM ET (US)     Profile for bigjohn1    
Mikuni and Keihin (both Japanese) have a reputation for a quality product. They are used extensively on various motorcycles as some others have suggested. Perhaps to get the three-star rating out of this engine, they had to go with an unusually restrictive carb - who knows. There are plenty of 170 MONTAUK owners who own this engine and don't seem to have these problems. Perhaps they can post their specific preventative maintenance regimen i.e. what works for them. Does anyone know the micron size of the factory under-cowling fuel filter? If it is allowing some very small sedimentation through, perhaps a spin-on additional filter will do the trick to help prevent this? I am sold on Quickleen and its ability in helping to prevent certain fuel-related problems. For all of the 90 4-stroke (carb) owners who have had no problems with their motor, what else are you doing (over and above the owner's manual stuff).
swist posted 12-21-2005 08:46 PM ET (US)     Profile for swist  Send Email to swist     
Would one use both Quickleen and Stabil?
bigjohn1 posted 12-22-2005 07:37 AM ET (US)     Profile for bigjohn1    
I could be wrong here but I can't see a need for BOTH Quikleen and Stabil simultaneously. Since Stabil is for preventing the breakdown of gasoline and associated varnishing of the engine internals, I have always considered it appropriate for winterization. Conversely, Quikleen (and like products from other outboard manufacturers) prevent the accumulation of deposits throughout the year as you run the engine. Some still put
Quikleen in the category of snake oil but the anecdotal evidence suggests it really does keep your fuel sustem cleaner. I use it regularly and my plugs have looked as clean as a whistle both times I checked/changed them. I hope more 90 4-stroke (carb version) owners chime in here with their individual experiences with carb problems. I am personally of the belief that a combination of Quikleen use and a good 10 micron fuel/water filter will eliminate these carb problems?
Maximus posted 12-22-2005 09:04 AM ET (US)     Profile for Maximus  Send Email to Maximus     
I run Techron with almost every tank of gas. There has been discussion that Quickleen and Techron are equivalent or almost equivalent products. Techron is far cheaper and sold at more places.

Towards the end of the season, I switch over to stabil as I may skip a weekend of boating every once in a while.

I've had zero problems other than a real hard time starting for the first time last season. Just think of the addition of Techron as you would adding TCW3 to a two stroke...something you have to do.

Here's the real question, what would it take to convert a carbed '03/04 to, wiring harness, electrical component/sensors, intake manifold, fuel pump, injectors...

I wonder if a kit exists.

Maximus posted 12-22-2005 09:08 AM ET (US)     Profile for Maximus  Send Email to Maximus     

Also, have you considered adding a Mercury fuel/water separator/filter to the fuel system? I did as a preventive measure for minimal cost.

I think these 4stokes need to be run and run often.

DIRTBIKERICK posted 12-22-2005 10:39 AM ET (US)     Profile for DIRTBIKERICK  Send Email to DIRTBIKERICK     
The mechanic who set up the boat put a water separator in the transom under the round white cover in the back, and again admitted to me about carb problems he had been having with my boat. Sounds like wads of yuk in enrichners and the use of cleaning agents are a common denominator here. Again i have been using stable since new, and changed the water separator filter once, I dumped out the gas from the filter, with no visual debris present. Called the dealer today, no answer yet on poor running, Thanks, rick
jimh posted 12-22-2005 12:33 PM ET (US)     Profile for jimh  Send Email to jimh     
Re using fuel additives: StaBil is a brand. I don't know that it works better or worse than other brands. The outboard manufacturers tend to have their own fuel addititives. For example, Bombardier has 2+4® Fuel Conditioner. The product is also labeled in French:


That word "carburant" seems particularly applicable here, eh?

The 2+4® Fuel Conditioner is designed to:

--stabilize the fuel system for one year of storage
--dissolve gum and varnish deposits in carburetors (and elsewhere)
--prevent corrosion
--prevent carburetor icing and fuel freeze-up

DIRTBIKERICK posted 12-22-2005 10:40 PM ET (US)     Profile for DIRTBIKERICK  Send Email to DIRTBIKERICK     
Here is the latest news: I called the dealer today. It seems like the motors that Mercury has looked at for this problem are mostly from California. Degraded fuel supply lines and debris entering the fuel system are the fault. The repair is to replace and upgrade the lines, clean out carburetors and go from there. This seems possible to me based on fuel quality these days. Still, I told the owner of the store I would like an EFI motor if Mercury will participate, or I wouold sell back to back the carburetor version and then buy an EFI. Any time after warranty expires and I still have poor running [problems], I'm gonna be kicking myself. Does anybody know of any [problems] with the EFI? Also, what about the new model 90-HP motors? Are they Mercury or Yamaha? Thanks, Rick.
bigjohn1 posted 12-23-2005 12:19 AM ET (US)     Profile for bigjohn1    
Rick - the 90-HP EFI Mercury outboard motors are still Yamaha powerheads, and we already have plenty of the 2005 models running here in Guam. I personally run a 2004 115 EFI, but this engine and the 90-HP are very much the same, aside from mimimal differences in bore and stroke. I have a little over 300 hours on mine and no [problems] to date. I'm keeping my fingers crossed.
bigjohn1 posted 12-23-2005 07:48 AM ET (US)     Profile for bigjohn1    
Oops, I think I meant to say 2006 versus 2005 for the Merc 90-HP motors having EFI. Whatever the year is, 2005 or 2006, I have seen quite a few already on boats here. I have asked owners I have run into at the boat ramps about them, and everyone seems to like them. I don't think any of them here have a significant amount of running hours on them, though.
jimh posted 12-23-2005 03:32 PM ET (US)     Profile for jimh  Send Email to jimh     
From all information available so far, for their 75-, 90-, and 115-HP four-stroke outboard motors, Mercury will continue to use a powerhead which has been manufactured in Japan by Yamaha and shipped over to Wisconsin for finishing as a Mercury brand motor. It is expected that 2006 will be the last year for this because Yamaha has been reluctant to sell these motors to Mercury, particularly after Mercury tried to hold their feet to the fire in the United States International Trade Commission (USITC) investigation wherein Mercury fought to radically change the outboard motor market in the United States by imposition of a tariff on Japanese imports.

Speculation about how Mercury will replace this important segment of their outboard motor line-up was ended when the head of Mercury Marine announced in September they would have new four-stroke engines coming out. See < > for details.

I don't know how successful you will be in your pursuit of a new motor with subsidy from either the dealer or Mercury. Although they are under some obligation to repair the motor while in warranty, I would be surprised if they offered much incentive to you to upgrade to the electronic fuel injected version.

It is astonishing that rubber hose fuel lines could degrade in such a short time. This motor was only a few months old. That seems outrageous that the rubber fuel lines are a problem. Oxygenated gasoline using alcohols have been common in the Midwest for decades. It seems hard to think that the fuel in California could be so hostile to rubber hose that it could damage it in just a few months.

handn posted 12-23-2005 08:38 PM ET (US)     Profile for handn  Send Email to handn     
I have carburetor problems with my 2 1/2 hp Yamaha. After several no run sessions at inconvenient times, I have stumbled on a couple of fixes that haven't been mentioned. Upping the float level a notch helps the engine run better. It may drop a star off the emission rating, but at least the damn thing runs.
Also there is a drain screw on the bottom of my carb and I drain the fuel any time I don't plan to run the engine for more than a couple of weeks. It is a pain to get at but much better than an engine that won't start.
I also endorse the idea of a Racor filter. My big engines are YamaMerc 225's. I like these engines a lot but the under cowl fuel filters are a joke and auxillary filters are necessary particularly here in Mexico where the fuel is not always up to snuff.
FISHNFF posted 12-24-2005 02:17 AM ET (US)     Profile for FISHNFF  Send Email to FISHNFF     
I have a 2000 Mercury 90 4 stroke that had problems from the start. Would die upon acceleration, but could be nursed to plane, where it would run great. A month in the shop and many Merc Tech visits and the carbs were synched and adjusted correctly.

I had one fuel related problem where it was running on only 3 cylinders. Clogged carb, even though it was run weekly. Interesting that just prior I ran out of Quickleen and ran about 40 gallons untreated. Coincidence?

I use Shell gas with Quickleen. The Quickleen really does help. I have 500+ hours, and it runs fine.

I have noticed my mileage has dropped some. The best I had new was almost 7MPG cruising the Bay. Now, normally used, it has gone down to under 5 from over 5. Maybe 20%. Change plugs annually, even though they look clean. Motor seems to run smoother afterwards. Took it into the shop last year, and told them to go through everything. Was told everything was within specs and good.

The mechanics have always cited small orrifices in the carbs for the problems. How in the world do the smaller motors survive, like the four cylinder 50? They gotta put almost half the fuel through their carbs! Those 9.9 kickers should get plugged if the air gets too thick! How often do most kickers get run? No complaints on these.

Have a friend who has thousands of hours on his twin Merc 75 4 strokes without a glitch regarding his fuel. But there was the making oil problem...


swist posted 12-25-2005 07:52 AM ET (US)     Profile for swist  Send Email to swist     
Well I just ordered the small Racor 10 micron filter/separator for small outboards (25 gph max). Looks like no big deal to install. Hopefully between that and Stabil, I will ward off the demons in these carbs before they appear.

And as to someone's qestion about an EFI upgrade kit - I seriously doubt such a thing would exist - there are two many differences - you just don't swap out the carbs for injectors. The computer is completely different - the air intake system is completely different (has sensors for oxygen flow, cold start system etc)

deepwater posted 12-25-2005 12:40 PM ET (US)     Profile for deepwater  Send Email to deepwater     
swist you are on the right track clean clean clean get the best filters for you car trk boat you can afford ,,its cheaper than a rebuild or a tow in
DIRTBIKERICK posted 12-30-2005 10:29 PM ET (US)     Profile for DIRTBIKERICK  Send Email to DIRTBIKERICK     
Okay so heres the latest info i have on the poor idling/running 90 merc carb version. It seem that the fuel line from the fuel tank to quick disconnect on the engine is degregating from inside, this includes the primer bulb and only on black fuel lines and not the newer style silver lines. The fuel then loses its volitily, turns cloudy brown and plugs the small passages in the carburators. The repair is to replace the line, clean the carbs and send you on the way. This info comes to me from my local merc dealer and is the same thing the dealer said where i purchased my whaler from. The only thing is the fuel in my water separator looked great and when i drained the fuel from the carbs it appeared to look good too. I'll let the dealer do the repair, take it home, let it sit for a month and then see what happens then. keep the faith right?, thanks, rick


whalerdude posted 01-12-2006 10:19 PM ET (US)     Profile for whalerdude  Send Email to whalerdude     
Wow! Am I glad I was able to be patient and wait for the first 06 Montauk to get to my dealer with EFI
fishinmishin posted 02-01-2006 04:21 PM ET (US)     Profile for fishinmishin  Send Email to fishinmishin     
Had a problem of no starts, poor idle quality etc. on my 2001 Mercury 90-HP four-stroke. My dealer was useless solving this problem. My solution was to drill out the access plugs and reset the idle screws to factory specs for initial adjustment.I believe its 2-2 1/2 turns from closed. When the engine was started the idle was quality was pretty good. After warming the engine Minor adjustment was made to fine tune the idle and also resynchronized the carb throttle plates with a vacuum gage.The engine has not had a single idle problem since (400 Hours) using the boat at 25 F temps also. Also logged the initial idle screw settings before adjustment they are as follows. #1 = 3/4 open, #2 = 1-1/2 open, #3 = 1/2 open, #4 = 1 1/4 open. As you can see, someone had a bad day on the assembly line. Yeah, I know you are not supposed to adjust the idle screws due to emmision laws, hence the plugs. I guess you could say, "when my engine won't run, I am not polluting."
maritime posted 02-18-2006 05:41 AM ET (US)     Profile for maritime  Send Email to maritime     
I am having the same problem as [Rick described above]. I have a 2000 Mercury 90-HP four-stroke. I've owned the boat for six months and never had a problem until this past month.

The boat sat for a month, its longest [period of non-use] ever. I put the boat in the water; the motor started right up. I got halfway out the harbor, went to throw on some throttle, and [the motor] died. The motor started right back up. I took [the boat] back to the dock, checked the fuel filter, and found it loaded with water. I dumped [the water] out and put [the fuel filter] back in, and I went off on my way. Then [the motor] died half way out agian. But [the motor] did not start back up this time. I was towed in and took [the boat] out to get a better look. Again, the filter had water in it so I knew I had some [contaminated] fuel in the tank. I drained the carburetor [float bowls] and water came out. Then, finally, I had pure fuel coming out. I gave [the motor] a crank and she started, but died shortly. I played that game for the whole day and gave up.

I told a buddy, and the first thing he asked was, "Do you have the SILVER fuel lines?"

I said, "Yup."

He gave me that look. So I took all the lines off and inspected them. Wow! Was I amazed!

These lines have a coating on the inside that just breaks off and goes right to the in-line filter which was loaded with little pieces. I figured [the fuel starvation problems I was experiencing were being caused by these broken fuel line pieces].

I replaced all lines, got a RACOR-brand water/fuel separation filter, and a new in-line fuel filter. Today I played the same game. [The motor] started right up, ran for a minute, and died. Started. Died. Started. Died.

I talked to quite a few mechanics, and they all say the same thing: "The jets in the carbs are clogged and need to be cleaned."

[The cost of a carburetor cleaning ] is around $250, here on Guam. Not too bad, I guess, for an island.

I am thinking that these fuel lines are what caused the problem, or I have very poor gas. But by next week, I should have a answer after I have the carburetors cleaned. I will let you know!--DAN

Also, if anyone has a idea [about the cause of] my problem, I would greatly appreciate your input. Thanks

jimh posted 02-18-2006 09:47 AM ET (US)     Profile for jimh  Send Email to jimh     
maritime--Thanks for you interesting narrative on problems with your 2000 Mercury 90-HP four-stroke motor with carburetors.

When you mention silver fuel lines, are you referring to the lines under the engine cowling? Or are you referring to the line used to connect the remote fuel tank to the engine?

Also, be sure to keep us posted on the outcome of your carburetor repairs. I hope they fix the problems with the extreme difficulty you are having in keeping that Mercury four-stroke running.

Finally, does the gasoline sold on your island contain methanol?

maritime posted 02-19-2006 12:07 AM ET (US)     Profile for maritime  Send Email to maritime     
NO its was basically a quicksilver kit with primer bulb and it was just from the remote tank to the fuel filter, and after to the bulb to a coupling right before the cowling then went to all black line inside the motor.

As to your question on methonal im not sure but will find out ASAP,........ anyways whats up with that? Also should i be running the higher grade gas or will 87 cut it?

bigjohn1 posted 02-19-2006 06:08 AM ET (US)     Profile for bigjohn1    
Maritime - it sounds like you had a few problems there. It seems like you took care of the water problem you were having by installing the new Racor. Because you still had water problems after installation of the filter, it seems your tank needed to be completely emptied and re-filled with new gas. It is fine to run the 87 pump gas in Guam through that engine - I have run it in a 115efi for nearly two years now with no ill effects. That is news to me on the grey Quicksilver fuel line kit, I think I will stay away from them now. For places to re-build your carbs, you have two choices - Coral Reef or Micronesian Marine. That is not a very difficult job though once you get the rebuild kits. If you enlist the services of one of the above shops to do it for you, good luck. It has been my experience for over 20 years now that getting really good mechanical service can sometimes be a crap shoot here.
carl lazar posted 02-19-2006 10:07 AM ET (US)     Profile for carl lazar  Send Email to carl lazar     
I have always put STABIL in the tanks and have never had a problem no matter how [seldom] I used the boat.
stockman157 posted 02-20-2006 07:52 PM ET (US)     Profile for stockman157  Send Email to stockman157     
I have a 90-HP four-stroke Mercury as well. Never had a problem at all with the engine. I let it sit a few months and had the fuel pump replaced, new oil, and new plugs. When I started it up to take it out it sounded rough. As I left the marina I accelerated and it konked out--it went to approximately 18 on the tachometer 91,800-RPM] and then stalled. When in neutral it sounds good and can be reved up all the way-up and over 60 [6,000-RPM]. It is only when it goes into gear that it stalls.. The mechanic says it needs a new rebuilt carburetor and wants $800. To me he shood have realized the engine was not in operational condition just by the sound of the engine. I have tried for the past week to run STABIL as well as other carburetor and engine cleaners and get the engine to get as high as 28 [2,800-RPM]. At times it seems about to break out but then sputters and dies. When is it time to give up and bite the bullet for the new carburetor? I do not understand why the engine gets gas flow nicely when in neutral and only encounters problems when in gear. I am not a mechanical person and am lost here. Any help would be appreciated.
bsmotril posted 02-20-2006 09:40 PM ET (US)     Profile for bsmotril  Send Email to bsmotril     
Your carburetor has multiple fuel circuits inside. Typically there is an idle circuit, a mid-circuit, and high speed circuit. The idle is a simple jet and air bleed. The mid jet houses the needle that meters fuel. The mid circuit operates typically from about 800-RPM on a Kehin carb, to around 4,000-RPM where the main jet begins to come into play. It sounds as if your needle and jet is clocked on the mid-range circuit. It is pretty easy to service a Kehin carburetor. The only tricky part is removal of the top cover. There is a thin rubber vacuum gasket just below it that is easy to tear, making the carburetor not function correctly. The good news is that it is cheap to replace, and damage can be avoided with a little care. Here is a link to a great article on the Kehin carb in a motorcycle application, how it works, how to tune it. It is very similar to the Merc carburetor.

This will tell you how to access and change the jets, remove the top cover, etc.


maritime posted 02-21-2006 04:04 AM ET (US)     Profile for maritime  Send Email to maritime     
I have not had the carburetors cleaned yet. I am still a bit curious to other things. I had a buddy come by and look at my 90-HP Mercury four-stroke outboard motor today. He had me start it and it ran for aproximately 30 seconds, then sputtered out and died. I told him after multiple experiments I noticed I could flood the carburetors. He put his hands on the intake and said one more time--it ran for about 15 seconds and died! He said [most of the time a restriction in fuel flow at the] intake is the problem; no suction on the intake, just barley noticeable. He thinks there is some kind of filter inside the intake or screen filters right where it connects to the carburetors. Is this correct? He is a mechanic for small boats but they are very old inboard diesels. I know he knows some stuff. I would like to believe him because it sounds like an easier fix. Or is he just plain old wrong? [Resolving the real source of the problem] is where I need your help. I read the manual and down, and I am not seeing anything about a internal air filter. I have very little experience with marine outboards so I do appreciate your help. THANKS
bigjohn1 posted 02-21-2006 08:24 AM ET (US)     Profile for bigjohn1    
Dan - there is no filter where your buddy thinks there is one. I strongly recommend you speak to Al Sizemore at Micronensian Marine and have him take a look at your engine. IMHO, It is a foregone conclusion your carburetors are plugged, but Al will do the job right and you'll have the peice of mind knowing your carburetors were serviced correctly. There are other competent mechs on-island but Al is the best in my opinion.
jimh posted 02-21-2006 09:17 AM ET (US)     Profile for jimh  Send Email to jimh     
I need a little help here with the articles being submitted. Please follow these simple guidelines, and you will save me a lot of time:

--Capitalize the first word of each sentence

--Capitalize the personal pronoun "I"

--Leave a space following a period before beginning the next sentence.

Thanks in advance for helping me to maintain the website with easily read articles.

maritime posted 02-21-2006 05:50 PM ET (US)     Profile for maritime  Send Email to maritime     
Thanks bigjohn1 I am going to call AL today. I have also heard that he is the best on island from many people. I have spoke to him a couple times,and he seems like a real nice guy. I will let you know how it goes. Thanks agian...DAN.
DIRTBIKERICK posted 04-02-2006 01:35 PM ET (US)     Profile for DIRTBIKERICK  Send Email to DIRTBIKERICK     
It's been a while since I wrote about my 2005 Mercury 90-HP caburetor motor and its poor running. I picked up my boat from the selling-dealer. They really did a good job of dialing-in the motor. They cleaned out the carburetors, synchronized and adjusted them, replaced the fuel lines from tank to engine. They also said the connecting linkage to the lower carburetor popped off. After returning home I ran the boat every day in the driveway for almost a week for half an hour minimum. The motor started and sounded better than when I first got it. Winter hit and the boat was covered up.

Three weeks ago I started it up. It ran, then died and would not restart, exactly as before. I made an appointment with my local Mercury dealer. He called me up at the end of the day and said the boat was running OK. He said the carburetors were out of balance and needed to be adjusted. Remember, the motor had not been used since it was last shut down and covered.

I came home, hooked up the water, and started the motor. It ran well for about 15 minutes, then started misfiring and back firing out of the exhaust.

At this point i am just boiling. Salmon season starts on Saturday and my $23,000 boat with 14-hours on the motor sounds like crud. I called the Boston Whaler dealer where I bought the boat. He said to write a letter to Boston Whaler telling them of my boat's running problems, and of how I have lost faith with it--which i have.

And with that, I now wait to see what [Boston Whaler's] response is. My only thoughts now are that it's lawsuit time. I want what I paid for: A boat the runs when I turn the key. Not a boat I have to run every two to whree weeks to keep the carburetors from gumming up. Not a boat I have to put Stabil or Quickleen in like a two-cycle--Which i have. Not a boat I have to worry about starting on the launch ramp, or a no-start with my kids onboard in the middle of the bay.

Anyway that is my story and I'm sticking to it. Bummed out Rick. Thanks.

rtk posted 04-02-2006 03:49 PM ET (US)     Profile for rtk  Send Email to rtk     
It's not a Boston Whaler problem, it is a Mercury problem. The Mercury dealer should be on the phone with a Mercury field representitive to resolve the problem. A dealer is responsible for resolving warranty problems, not the boat owner. The dealer has way more corporate connections than you do.

My first call would be to Mercury Marine corporate, not Boston Whaler. Be nice, patient and leave emotion out of it, and you may get somewhere with Mercury.

Is there another Mercury dealer in the area? I would get a second opinion. Carburetors do not become out of adjustment from sitting for the winter.


jimh posted 04-02-2006 04:28 PM ET (US)     Profile for jimh  Send Email to jimh     
It is clear that your Mercury outboard motor has problems. It is entirely reasonable to insist that a new motor be able to start and run reliably.

We also seem to have an issue. At issue here is who is responsible for providing a remedy to this problem. Is it:

--the selling dealer
--the boat manufacturer
--the engine manufacturer

In my opinion you should seek a remedy from the selling dealer. He is the provider of the goods which seem unsuitable or fail to provide the expected serviceability. Attempts by the selling dealer to ask you to seek a remedy with other parties are not appropriate. You gave your money to the dealer, not to Boston Whaler or to Mercury Marine.

Have an attorney read your sales agreement with the selling dealer. If the sales agreement provides that you must seek a remedy with the manufacturer for certain problems, then you should pursue a remedy with the manufacturer.

Whether you should seek a remedy for the problem with the outboard motor with Boston Whaler or with Mercury Marine goes to the question of mandatory tie-in sales. Purchase of the boat was made with a mandatory tie-in sale of the Mercury Marine outboard motor. I am certain that the dealer's position will be that he bought the boat AND the motor from Boston Whaler, and this may be guidance for you for from whom to seek a remedy.

It is probably best to not involve a second dealership in this matter. If more than one company is providing service and repairs, this may complicate the dispute and make resolution more difficult.

An investment of $24,000 is a significant amount of money. There is no reason to accept less than expected performance from the product you purchased.

Rob007 posted 04-08-2006 10:19 PM ET (US)     Profile for Rob007  Send Email to Rob007     
I own a Yamaha 2-stroke marine engine, and they recommend using a fuel conditioner/extender (like Sta-Bil) year around. However, during the season, they recommend using one ounce for every two gallons of gas. Then for winterizing, Yamaha recommends using the one ounce for each gallon of gas. It's only logical the same would apply for four-stroke outboards. My Yamaha marine dealer's service manager agrees. What do you do with a half tank at the end of the season ... do a little basic math with the quantity of Sta-Bil (I use Pennzoil's marine fuel conditioner) and keep that tank topped off over the winter--and be sure to run the engine so it ingests the "winterizer strength" of the Sta-Bil. That's what you want in the carbs.
joenewton posted 04-21-2006 09:46 PM ET (US)     Profile for joenewton  Send Email to joenewton     
I just purchased a 2004 Montauk with a Mercury 90hpELPT 4-stroke. The boat had seldom been used and only in fresh water. I plan on using the boat at least 200 days a year for several hours each outing. I purchased the boat from Marinemax and the motor still has a year and a few months warr. It started well and seemed to run strong. Maybe I should think about an ext. warranty and add some fuel/anti-gumming mix? Is this a major problem everyone is having? I was led to feel that this was a very strong, dependable motor. Several folks at various marinas said the motors were "bullet-proof" and a "yamaha in black". Well, my boat is in dry-storage beside marinemax so I don't have far to go for problem fixing. I just hope that this a minor thing that is not a widespread occurance. Thanks for any input. A former 1987 15CC owner.
jimh posted 04-22-2006 01:38 AM ET (US)     Profile for jimh  Send Email to jimh     
Joe--In our business we have a saying:

"It takes ten atta-boy's to cancel one oh-shoot!"

This is probably very true in on-line discussions. There may be ten satisfied owners for every one that complains.

I do not have any real data to share with you about the Mercury 90-HP engines with carburetors and how common it is to have trouble with them. By the evidence of this and several other discussions, you can say that it is not unheard of to have problems. Does everyone have problems? Most likely not, or there would be more horror stories to read.

bigjohn1 posted 04-22-2006 08:43 AM ET (US)     Profile for bigjohn1    
Joe - there are scores of boats running around out here in Guam with that very engine. I try and make it a point to ask those owners if they have had any carb problems. Not one has had any complaint on performance or more specifically, on their carbs. Perhaps the common denominator here is level of use - meaning since the engines are used regularly, they don't have problems. I think you are going to love that engine.
joenewton posted 04-22-2006 05:28 PM ET (US)     Profile for joenewton  Send Email to joenewton     
Thank you for your response. I feel better about my purchase that was made yesterday, 4/21. I traded in my 1987 15CC with a 1998 50hp Johnson. Many things new and replaced, all done to Whaler specs on this boat. It almost like a new 1987 15ftCC. Marinemax at Wrightsville Beach, NC will have the boat. Let me know if interested and I'll tell you who to contact. I have all service/replacement statemets. Not a sell's pitch, just want the boat to have good owner., Thanks, JN.
Barney posted 04-22-2006 05:48 PM ET (US)     Profile for Barney  Send Email to Barney     
Yep, the Mississippi Department of Marine Resources uses this outboard. They use large filters though and churn up huge amounts of hours. Usage and advice given already should keep it going. Just as a note, After Katrina mine ingested water due to bad fuel and overwhelmed the little filter, twice. My screwup. I successfully got mine running great again without a carb rebuild but it took some patience. I now have a big filter. Jim
mikeyairtime posted 04-26-2006 05:06 PM ET (US)     Profile for mikeyairtime    
Put a fuel shut of in and run it out of fuel every time you run it. When you store it drain the carbs by loosening the little screw plugs on the bowls after running it out of fuel. My two year old 90 4 stroke fires every time when I do this. Most recent was a 6 month storage due to a broken collarbone that refused to heal and the resulting sugery. I charged the batteries pumped up the fuel primer and it fired instantly. You can join the debating society of why or why not you should do this or just start doing it and enjoy jour boat. It will hurt nothing.
Barney posted 04-26-2006 07:12 PM ET (US)     Profile for Barney  Send Email to Barney     
Mikey, That is a great idea. If you got it to run after 6 months that is the ticket. I know more about these carbs than I want too already. I'm currently running premium too. Jim
David Livingstone posted 04-26-2006 08:40 PM ET (US)     Profile for David Livingstone  Send Email to David Livingstone     
Folks, I run a 1999 F100 Yamaha. The first thing my Yamaha dealer told me was to only burn regular gas in it. They said that burning premium would bring me trouble. Six months later, I'm 2000 miles south of the border and have problems with the motor cutting out at 4000 RPM (replaced CDI when I got home). I took it into Tuppen's Marine in Lake Worth, Florida. What's the first thing they asked me? "You're not burning high test in it, are you?" They also told me to only burn regular fuel.

This bags the question. Since Yamaha and Merc carburated 4 strokes are nearly the same engine, does Merc also recommend only burning regular gas and staying away from the higher octanes?


Barney posted 04-26-2006 08:56 PM ET (US)     Profile for Barney  Send Email to Barney     
Wow hope not, just started using premium. Here is what my 2004 manual says:
...minimum posted octane rating of 87. Mid-grade automotive gasolines that contain fuel injector cleaner are preferred for added internal engine cleanliness.

Looks like the opposite of Yamaha recommendations. Jim

mikeyairtime posted 04-27-2006 09:21 AM ET (US)     Profile for mikeyairtime    
I run the Chevron regular.
bobeson posted 04-30-2006 12:23 AM ET (US)     Profile for bobeson  Send Email to bobeson     

After I had problems with fouled carbs on my 2003 Merc 90hp four-stroke last spring following a 4-month period of non-use (and no fuel stabilizers added), I presumed that my foolishness of not adding fuel stabilizers last fall would doom my carbs to another round of rebuilds this spring. This month, following my longest period of non-use ever (almost 8 months - we have another new baby in the house), I just assumed that I would need another carb rebuild and didn't even try to start the motor until I'd rebuilt the carbs. I pulled the carbs and started to rebuild #4 (the bottom carb, the worst one by far last time around for some reason). It looked remarkably clean, however, with none of the visible gunk that fouled my carbs last year, only a faint sheen of what I presume was the shellac from evaporated fuel.

Rather than risk damaging any of the seals on the remaining carbs, I deciding to put the carb assembly back on the motor and see if it would run OK before I rebuilt the remaining carbs. I put some carb cleaning additive in a new tank of fuel and started the motor. It was hard to start and ran rough for a while, and died often. I upped the idle a bit to help keep it running, and then let it run at about 2,500 RPM for twenty minutes or so. It sounded a lot better after that, so I took the boat out on Monterey Bay and caught limits of salmon in two hours. The motor is running great now, and starts up cold, and isn't giving me grief except for the slightly high idle, which I will dial down before the next outing.

I'm not sure what to make of this. I am starting to suspect that the story about the lining of some of the silver-colored fuel lines dissolving and fouling the carbs might hold water, as it were. In any case, it would seem that normal non-use does not result in the serious fouling I experienced last year, and perhaps my problems last year were a one-time event (I hope!). I still had minor troubles with rough running at first this year, but anything that can be fixed by dumping a bottle of goo in my gas tank is no big deal in my opinion.

For what it's worth, I run mid-grade fuel as recommended by Merc for this motor, and I rarely use extra additives.

Barney posted 04-30-2006 08:35 AM ET (US)     Profile for Barney  Send Email to Barney     
bobeson, Looks like you've pulled your carbs a couple of times. I have the manual and would rebuild myself if I have to in the future. The bottom carb is hard to reach to drain too. How long did it take you to remove the bank of carbs in one piece. When you look at the carbs it's hard to invision the way they come off. Any hints would be appreciated. Jim
bobeson posted 04-30-2006 12:35 PM ET (US)     Profile for bobeson  Send Email to bobeson     

Jim, I think it took me around an hour to pull the carb assembly the first time around, and perhaps 30 minutes or so to pull them the second time. It's really pretty easy. There are a few difficult-access bolts, but most of it is straightforward. The worst bolt access is solved by moving the throttle linkage out of the way just so, which took a little fiddling to figure out both times, but now it seems easy when you know how it goes. The other difficult bolts are reachable with a universal-joint and extensions. Make sure you study the hose routing while you disassemble, as some of them are a bit counter-intuitive on reassembly. Also be careful of the inline filters on the fuel lines right at the carbs - they fall out when you pull the fuel lines off, and they are small and easily lost. I was able to re-use all of the seals both times, but some of them are fragile so be careful when you open up the carbs themselves. The only items I had to replace were some zip-tie hose clamps. In the past I've always bought carb rebuild kits when I opened up carbs, but the Merc kit price is astronomical on these, and you really don't need it if the carbs are gummed but otherwise in good shape. Good luck!
Barney posted 04-30-2006 07:04 PM ET (US)     Profile for Barney  Send Email to Barney     
bobeson, Thanks alot, that is excellent info. Jim
joenewton posted 05-01-2006 09:18 PM ET (US)     Profile for joenewton  Send Email to joenewton     
I have now run my new 2004 Montauk 3 days in a row for a couple hours each day. The 90ELPT Merc. seems to be running fine. I've ran at 2000rpms for about an hour with my wife and then several times running at a steady 4500 out to the inlet and back. I did notice that around 2100 the motor seems to "rattle" like its clogging, but as I increase the RPMs to plane it begins to run fine. As soon as I use the rest of the gas in the 27gal tank I'll use the Quick-leen(spelled-right?) stuff on my next tank fill-up. I live in North Carolina so maybe area might play a role? Thanks again for all the advice that has come in on this subject.
bsmotril posted 05-01-2006 10:58 PM ET (US)     Profile for bsmotril  Send Email to bsmotril     
That rattle might be pinging or detonation, which is extremely damaging to a motor. I say that because it happens right at the rpm range where load is highest as the hull transitions up on to a planing configuration. Some of the causes of pinging are lean carburation (either from jetting uses, or clogged fuel passages in the carb), too much ignition advance, or carbon deposits in the combustion chamber. I would avoid running the motor in that RPM range where the rattling noise occurs, espcially if it sounds like marbles in a coffe can. BillS
whaler1234 posted 09-13-2006 11:01 PM ET (US)     Profile for whaler1234  Send Email to whaler1234     
My apologies for bringing up an old post.

After searching thru the posts for 170 carb problems, I came upon sosmerc's post re: the granular, sand or rustlike material found in the stabil container.

I too have found an alarming amount of material in my container of stabil. In fact there is so much material it has clogged the small measuring tube to a point I cannot squeeze any fluid into it.

I will try to get a decent picture of it, but for now I am discontinuing the use of stabil and switching to startron.

This bottle has only been opened a few months and I don't recall the material being in there when I bought it.

It's also interesting that my shop had just recently rebuilt my carbs and informed me they had found sandlike material in my fuel tank and filter.

Mijoy posted 05-02-2007 09:55 AM ET (US)     Profile for Mijoy  Send Email to Mijoy     

I'd like to resurrect this thread now that we are faced with another spring boating season and, frankly, because I have developed this problem.

First I'd like to comment on a post where the poster asked a question about small filters that are actually inserted into the carb input nipple (totally invisible unless the hose is removed). The poster wondered if these filters actually where there and received a reply that they were not there. Well on my engines 1999 F100 Yamahas, they are there.

I used my engines all of last year without a problem. Following the last trip the boat sat in my yard for about two weeks when I had hoped to use it again. Both engines appeared to running poorly. I added stabilizer to the gas tanks (2 50 gallon taanks each seperate systems) and winterized the motors. Just a few weeks ago I tried starting them. Both ran terribly.

Here is were it gets interesting (and frustrating). I removed and cleaned all four carbs from the port side engine. I also replaced the needle valve assembly (I didn't buy an entire replacement kit). I also didn't remove the "blind plug" and the low-speed needle jet (didn't want to introduce any problems I didn't already have). But I did soak the carbs, then spray with carb cleaner blow out and reassemble.

The engine started (last Saturday) and seemed to run well. I took it through it's operating temp range (cold to warm) and it appeared to idle and throttle up and down well.

Yesterday (two - three days later) I started the engine again and it was running poorly. It appears okay for 1-2 minutues (I'm guessing it is during the time the primer is injecting fuel into the carb throat. Once it begins to warm up it goes steadily down hill.

Has anybody witnessed similiar symptoms? The fuel filters, visably, look okay. If there is gunk in the system it is invisible to the naked eye.


Dick E posted 05-02-2007 08:11 PM ET (US)     Profile for Dick E  Send Email to Dick E     
My fishing buddy has 90 4 stroke carb, The dealer told him to put stabilizer in his fuel ALL YEAR ROUND. He does and has no problems.It reduces or eliminates gumming
ronshire posted 05-29-2007 10:47 PM ET (US)     Profile for ronshire  Send Email to ronshire     
there is a kit for these carburated mercury four strokes now available to rejet them. they won't meet emission standards and may not be available for motors still under warranty.

you will most likely have to tell the dealer they are available and for them to call mercury tech hotline. i got this info from a dealer that was working on a 40 hp and had these similar problems he couldn't solve

Walleye Mike posted 06-25-2007 06:53 PM ET (US)     Profile for Walleye Mike  Send Email to Walleye Mike     
I have a 2000 Mercury 90-HP four-stroke, and I'm having the same carburetor problems as some of the other boaters. Has anyone with a four-stroke solved their problem? I have fuel and start and stop problems. It's at the dealers for the fourth time. I hope somone out there can help. Mike
outragesteve posted 06-26-2007 04:37 PM ET (US)     Profile for outragesteve  Send Email to outragesteve     
I had similar problems w/ my twin F100's. After total frustration and countless hours, I found the problem. Both engines would run, die, sputter, not turn higher rpms, etc. i rebuilt the carbs 3 times each! (I can get them off in 15 minutes: Pull the intake and carbs together. I changed fuel lines, filters, installed Racors, drained the fuel tanks, etc. Still same problem. Then I hooked up a brand new portable tank (at the Racor input) and the engines ran perfect! Re-plumbed in the internal tanks and they would not run right. I drained the fuel (80 gallons) again, and refueld. Bingo! The problem was the fuel (2nd load) was about 2 months old. I strained it through filters and it was clean. (here in Hawaii we havem 10% ethanol) There was no "phase" seperation or water. It was just bad gas. Fresh fuel is a must on these engines. I then had problems with my lawn mower: Yes, using the gas from the boat. Drained the tank, added fresh fuel, and my mower was happy again. Next time I will use a portable gad tank first and save alot oftime and agony!
Walleye Mike posted 06-26-2007 07:56 PM ET (US)     Profile for Walleye Mike  Send Email to Walleye Mike     
outrageous Steve,Thanks for the input.One question do you use sta-bil or any product in your gas?I just put $1000.00 at the dealers to re do my carbs.He did find a Manufactur defect in the block, gouges etc.But of course Mercury did not stand behind their product because they said I must have done it.Even though it had the original head gasket.And my dealer is the only one who has serviced my motor.Thanks again Mike
Ed Z posted 06-27-2007 08:59 AM ET (US)     Profile for Ed Z  Send Email to Ed Z     
I have been running 4 stroke outboards for over 20 years now (Bearcat 55hp and Bearcat 85hp) with carbs... The problem I think of when I read through many of these entries is the gas line... Not the tubing itself, but rather the quick disconnects... The Bearcat setup uses the old style Chysler connecters that have 4 o-rings to make the seal... What I have found is that these o-rings quite easily can be damaged (especially if dry) and cause a vacuum leak... I have been quite surprized just how little of a leak can cause many of the above mentioned problems... The odd thing is that each time I had no sign of fuel leakage at the connection... I have since then obtain many replacement o-rings and do so each year at the begining of the season... Also I use a Q-tip with vasoline to lube the orings prior to any long term lack of use...
Since taking on this practice, I have yet to experience further fueling issues... I have use year old fuel as well with no problems too... I do run my carbs dry each and every time I trailer the boat as well... This applies to both new and old tech carbs... The originals were Tillotsons (30 plus year old design) and the new are Edelbrock 38mm side draft (new tech design)...

Just my two cents worth here; flame suit on and ready...

Sailor Rob posted 12-07-2007 04:45 PM ET (US)     Profile for Sailor Rob  Send Email to Sailor Rob     
I add Quickleen to every tank of gas (Lukoil 89 octane or sometimes Shell 89 octane)for my carburated 2005 Mercury 90 4 stroke and have never had a problem running this engine. We do a lot of water skiing and go out in the 170 Montauk (which I bought new) almost every day over a 12 week season. Never any hesitation or stalling. Never any water in the still original fuel filter.

I run the engine 50 to 60 hours during the summer and store it for 8 months in a garage here in New Jersey. I add Stabil to the last 6 gallon tank and let that run down to two gallons or less before laying up the motor for the winter. Motor is stored in vertical position. I do not fog. In the spring I add fresh gas to the tank before our first run. Starts instantly three years in a row.

whaler1234 posted 05-13-2008 05:45 PM ET (US)     Profile for whaler1234  Send Email to whaler1234     
Hi Guys,

Its been over a year since I have posted/checked in here. I'm looking for some advice.

My 2004 carbed merc on my 170 has been stored (treated w/ stabil and quickleen) for over 8mo. I decided to take it out this past weekend. I had problems running in low rpms (2-3k) and idle would cut the motor. High rpms ran fine. I'm thinking the idle jets are clogged again.

This will potentially be my second carb rebuild in two years and will cost me $1000.

Here's my question: Being a new father, there are times when the merc will be stored for long periods of time.
I am thinking of purchasing a brand new EFI motor to replace my carbed motor. I haven't been keeping up w/ the latest news, but do the new EFI's store well? (8-12mo).
Are recent 170 owners seeing the issues us carbed owners have seen w/ the carbed 170's? My other option would be to sell my 04 and get a new 08 170 if it came out cheaper that way.

If the new EFI's don't have any "long term" issues, not having to worry about being stuck in open water would justify the purchase.

I remember reading some posts stating the EFI system can get clogged as well. I would love to hear any testimonials from new 170 EFI owners.

Thanks all,

Mijoy posted 05-28-2008 01:03 PM ET (US)     Profile for Mijoy  Send Email to Mijoy     

Hi Whaler1234,

I'd suggest, if you are in the position to purchase new EFIs that would be the choice to take.

I have 2 1999 Yamaha 100hp 4-stokes. I have constant problems with carburation. I was able to limp thru last season after rebuilding them. Although they were not running good. I too have problems mostly in the 2-3k range. At the end of last season I left the boat in the driveway for three weeks (in early nov). I was hoping to go fishing one last time and I started them up in the driveway. Once again they were running horrible. Again, this year I have taken them all apart and will try to limp thru another season. If I am able to limp thru this year, next year I will be relacing these **** boxes.

I do not believe the EFIs will present you with the same difficulties. I think this problem is largely inherent in these carbs/engines. The jets are very small and clog easily. Combine this with the fact that they are very sensitve to ideal tuning and they are constantly a source of problems once the factory tuning has been disturbed.

Best of luck,

jimh posted 05-28-2008 01:24 PM ET (US)     Profile for jimh  Send Email to jimh     
Follow up comments for whaler1234 should go to the separate discussion he has begun on this same topic at

HVGBMACH1 posted 06-30-2008 11:01 AM ET (US)     Profile for HVGBMACH1  Send Email to HVGBMACH1     
Hi, first off I read some post on starting problems with 90hp 4stroke mercs. Trying to start your engine in shallow water with engine tipped up a bit will be tough to start. The engine starts much better tipped all the way down.Also everybody around here uses a separate water seporator.
And I have a question for you guys, my 2003-90 4stroke merc is really hard on gas (burning almost double what it should be). I had carbs cleaned and set up (basic tune up stuff done), inside coil replaced, thermostate replaced. Engine runs fine, seems normal but just burn alot of gas. There are about 3 or 4 of these motors around here and nobody is having this trouble but me. Anybody see this problem before or know anything i can try?
fishinchips posted 06-30-2008 11:12 AM ET (US)     Profile for fishinchips  Send Email to fishinchips     
What do you think your mileage or gph is?
Roughly you should be getting around 4mpg to almost 5mpg. For sure over 3mpg.


HVGBMACH1 posted 06-30-2008 01:11 PM ET (US)     Profile for HVGBMACH1  Send Email to HVGBMACH1     
Hi, Fish
Thanks for the reply. I would say approx. 3 mpg.
This is a guess ( my cabin is approx. 18 miles away and I'm burning about 11gal. down and back, give or take a gal.)
It seems to have gotten worse since last summer. But again, the motor is working fine.???
Tohsgib posted 06-30-2008 01:35 PM ET (US)     Profile for Tohsgib  Send Email to Tohsgib     
My 115 EFI would only burn about 6-8 gals on that run.
sjp1311 posted 11-10-2008 10:03 PM ET (US)     Profile for sjp1311  Send Email to sjp1311     
Ok, I am not a Whaler owner, but I once was. Best riding boat, I ever owned.

Sorry to rehash old topics, but...

I am now a tooner(25' Crest with a 90 Merc, 4st, carb).

Engine/boat is 2003.

I am having the exact same problems that you guys are, except now the engine won't fire at all. I did not know all these little things.

I recently winterized my engine, oil looked like it had been ran in diesel for 200k, staight black. The oil change only had 25 hrs.

Today, I pulled plugs, they were covered in crap, oily carbon stuff, so I cleaned them up. Still no fire, tried everything.

I sprayed carb cleaner in engine, ran great, until it was used up, could not get to fire on gas. I did try to run a 'hot' tank through the engine, never got it to fire, cleaned tank topped off with premium, no ethanol, and a can of Seafoam. Still nothing.

I will try to drain bowls, and retry the fireing sequence.

Where is the best place to get this service manual.

I did call the original stealership, the engine had been in 3 times in a year to 'correct' these same issues I am having today.

I am also calling Mercury to get some advice.


riverdrone posted 04-09-2009 06:03 AM ET (US)     Profile for riverdrone  Send Email to riverdrone     
[Revived this discussion about problems with the Mercury 90-HP FOURSTROKE with carburetors in order to change the topic of discussion to a 90-HP motor with fuel injection. Please begin a separate discussion on that motor because it does not have carburetors.--jimh]
steve gibson posted 06-19-2009 07:19 PM ET (US)     Profile for steve gibson  Send Email to steve gibson     
[Revived this discussion about problems with the Mercury 90-HP FOURSTROKE with carburetors in order to change the topic of discussion to 60-HP motors, problems with water in fuel, and advice about oil brands. Please begin a new discussion on those topics as they are not on our topic of problems with the carburetors on 90-HP FOURSTROKE Mercury motors.--jimh]
whaler1234 posted 07-01-2009 11:07 PM ET (US)     Profile for whaler1234  Send Email to whaler1234     
Since these are Keihin branded carburetors, does anyone know if one can get rebuild parts thru a motorcycle shop rather than thru Mercury?

FlyerB posted 08-07-2010 02:41 PM ET (US)     Profile for FlyerB  Send Email to FlyerB     
[Changed TOPIC to something other than the carburetors of a Mercury 90-HP motor. This topic has been moved to a new thread. Please do not revive old threads only to change their topic.--jimh]

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