posted 02-16-2013 04:09 PM ET (US)        

February 2011: bought an awesome 1998 17 Alert/special service Montauk from CWW member Fishnff/Brian, with a 2000 Mercury 90hp carbureted FourStroke, knowing only that these carbureted motors like/need to be run often. It already had/has a large external 10 micron water-separating fuel filter.

Feb 2011-Fall 2011: started it and ran it on the muffs in the driveway more or less weekly, certainly no less often than every other week, but mostly weekly. But did NOT take it out in the ocean very often where I could put some load/speed on it, (and I think that is important). By late fall, it was not always liking full power. It would either stumble on and off at full power or simply get "stuck" and not even go into the full power circuit. Usually in the cold rough Pacific, mid-power is all you want.

Fall 2011: I spazzed (term of high literacy) and assumed clogged carbs right off the bat, and with more mechanical skill than sense, tore the carbs off and disassembled them, cleaned them, and put them back together, without first doing any other diagnosis. Discovered one of the carbs had a badly gunked-up, sticky needle. I sort of cleaned it (the deposits were very hard to remove), so I just unstuck it, and called it good... definitely not good surgical technique. I should have replaced it. It started at the first crank, to a stumbly but reliable idle. I did not have a balancing tool, and did not realize the importance of one. Fortunately, I did not disturb the settings too badly so it ran OK (but not like you would want a brand new engine to run). I continued to run it on the muffs every week or so, but did not take it out in the ocean due to being tied up with other priorities.

Spring 2012: Took her out in the ocean and she would not get out of idle without dying. I started to get more serious about the importance of proper balancing (of the four carbs), and on the GREAT advice of CWW member sosmerc, got a very good balancing tool for less than a 10th of the cost of the digital vacuum mate. It is the Motion Pro products, Sync Pro. And it is ~$100. Talk to me before you buy one though. I did a quick and dirty balancing job, (turned out I did a poor job, but it was my first time). Was still getting random stalling and not able to get to full power. So I got discouraged and "shelved" my interest in this boat and concentrated on other things for a few months.

Fall 2012: Stripped off and cleaned the carbs again, this time paying more attention to blowing carb cleaner through all the little passages. Started it up just fine and ran it on the muffs once a week. Took it out on the ocean and wouldn't go to full power. Got discouraged again and shelved it again for the holidays.

January 2013: Decided to get more serious about balancing it right. Only this time it was VERY hard to start. Weird because prior to that in the fall, it started right up to a stumbly but reliable idle. So I screwed the idle speed screw all the way in (to full fast), and eventually got it started. So now I have a problem with cold starting, but it runs ok once warm. Great, another problem. Removed, cleaned and tested on battery the cold start enrichers, they were fine. Still hard to cold-start. Another trick I used once it was _barely_ running was to loosen the set-screws on the TPS and advance it by twisting it. That worked very will (BIG clue, btw), in getting it warm and stable idling. This time, I hooked up my balancer tool (the Motion Pro SyncPro), and did a thorough job balancing it. It was purring along pretty nicely. I was confident. Took it out in the harbor with kid, wife and buddy, and putted along hither and yon inside the harbor in quiet four-stroke bliss. Then we left the harbor and when I put the coals to her? Stutter-stumble-die, stutter-stumble-die. After a few times of that, even the idle began to become unstable and unreliable. @#$%^&*!!! By now though, I LIKE the novelty of the quiet idle and great fuel economy of this big heavy four-stroke. Hey, it's a Whaler, not a speed boat. I already have fast boats with light powerful (reliable) carbureted two-strokes for going fast. That's not what a Whaler is for though, and I have no interest in making it that way. Stripped all the carbs off one more time, (by now, it's easy), for a thorough cleaning and this time, I ordered new needles and seats from Yamaha. These 90hp Mercury powerheads are in fact IDENTICAL to the Yamaha F100 powerheads of the same year, and shockingly, the Yamaha parts were a little cheaper. Both Keihin BCF carburetors with identical jetting. Put it all back together again and? BAM! Hard to start. Basically will not cold-start unless I screw in the idle speed screw and fiddle with the TPS once it "catches" into a barely running idle. When it warms up, it idles pretty nicely and I back out the idle speed screw and set the TPS to full clockwise (it has slotted mounting screws), the way the manual says to, (hint hint). By now, I've cold-start-nursed it into a steady warm idle a half-dozen times. I have almost no fear at all of a no-start. Fear of "no-start" was a recurring theme in quite a few of the other threads on here, so this is BIG news to me and even with problems, makes things HUGELY better for my confidence in this thing.

Mid-February 2013 (yesterday): The day before yesterday, I had yet another hour or so of good running on the muffs after what has become a standardized ritual getting it cold-started. So yesterday, I take the boat down to the harbor by myself (no wife and kid while it's still risky). While tied to the dock, I try the standard, turn the key as if it's a new motor, and it will not start, just cranks and kicks. No biggie. It has been this way for a month now. I pull off the cover and do my usual tricks to get it started and warm and it works just like it has for the last month. Now I've got a warm idle. It is important to know that BOTH advancing the TPS and screwing in the idle speed screw will increase the idle speed. The manual says the TPS should be all the way clockwise in it's slots, but now I am suspicious of it, so I set it to a point where it very slightly speeds up the idle, then I compensate by turning the idle speed screw back out far enough to get a proper idle, and head out into the harbor. Putting along through the "no wake" zone goes well. When it's time, I put the coals to her and? Stumble sputter go, stumble sputter go. On plane, but not quite wanting to get into or stay in, full power. But someone else in another thread talked about how he soldiered on this way until his finally "cleared up", so I decided to keep her floored and see if she would clear up. But my carbs should have been clean. I just did them a couple of weeks ago. After a few minutes of "stumble stutter go", "stumble stutter go", waiting for things to "clear up", I realized I didn't have my lifejacket and headed back to the dock to go get it out of my car, (I brought it, but I left it in the car). THIS time, on my growing hunch that the TPS is bad, I moved it a little more counter-clockwise, which advanced the idle speed a little faster, and turned the speed back down again using the butterfly screw. Remember, the manual says the TPS should be all the way clockwise. So, I putted back out nicely through the no-wake zone as before. When it was time, I put the coals to her. And? This time she explodes up to full power!!! No more "stumble stutter go". Just "go". I ran her hard at 4000-5500 rpm for 20 minutes straight without a single stumble. Woohoo. Satisfied, I putted back through the no-wake zone to the dock at low power. At the dock, at full closed idle, she didn't quite want to keep idling, so I pulled the cover and turned in the idle speed screw just a wee bit, and? Purrrfect :) This motor is very sensitive to slight adjustments. And they all affect each other. Lot's of thoughtful fiddling is rewarded with this motor.

So now what? Something is still wrong. At the very least, I am not getting the timing advance I am supposed to be getting on cold-start. I do not know if it's the fault of the TPS, or a temp sensor, or the CDI itself (though I hear these particular CDI's are pretty reliable). As for the TPS, I do not know if this a rudimentary, two-position, binary, hi-lo TPS, or if it reports a continuously varying voltage from the beginning to the end of it's sweep. I also don't know if the CDI sets timing on a smooth curve, or has a programmed "step", where it goes from advanced to retarded to advanced again or what. If this were an EFI system, I would know. So either the TPS is bad or something else that affects timing is bad. I don't know which yet.

In the mean time, I have found an uneasy peace with this motor. I feel like I know it's tricks, and know what to do when, with it, so I don't end up stranded. And I'm VERY happy with that. (Hear that, Brian? If you read this, do not feel bad for me. I am very happy with my purchase.) I am learning things about this motor hand-over-fist, and it is fun learning. I have high hopes of getting it running like new eventually, but in the mean time I can still use it just fine as it is.

More to come...

posted 02-18-2013 02:36 AM ET (US)            

It's been pretty good when I had it, so can't really comment on how to debug.
When I first got it, right off the bat, I had an acceleration problem that was solved by float synching the carbs. Funny, as it was fasted then. I hit over 39knots (solo with tide) with a 19" prop, but had to nurse onto plane.
A 17" prop gave me 35 +knots. The 15" trolled best.

I ran Mercury Quikleen regularly. I believe in that stuff, and make sure you have good gas.

posted 02-18-2013 01:51 PM ET (US)            

BTW did you ever have the valve clearances checked and adjusted?

posted 02-20-2013 07:36 PM ET (US)            

Have you used Marine Sta-Bil at any point during this process?

posted 02-21-2013 12:11 AM ET (US)            

Hang on for more updates soon... With these motors, notwithstanding the lore, not every problem is due to clogged tiny passages.

posted 02-21-2013 10:05 AM ET (US)            

Carburetors can be very frustrating. In the sixties while stationed in Germany I did a lot of Porsche 356 tuning which for the most part included carburetor balancing. The SCs were the most challenging. After some poor results I finally got the hang of it and had a lot of fun while making a few marks in the BOQ parking lot. Eventually I became so busy I had to price myself out of the market in order to have some time to enjoy Germany. It seemed that every young single officer in the area had a 356. A background in racing Ford flatheads with triple carburetors was an immense help.

posted 02-21-2013 03:36 PM ET (US)            

I've never really had a problem (bit of rough idle & balky acceleration one season, but that was fixed by chopping off the mixture screw seals and adjusting a bit richer).

Peter, I wish I could share your enthusiasm for solving these problems. I'm out in the cold unforgiving ocean a lot, sometimes with small kids, and I have to say, the slightest burp (always something other than the engine, most probably my imagination) makes me nervous.

posted 02-21-2013 07:05 PM ET (US)            

Don't get me wrong. I like EFI as well as the next guy. My race car is EFI, and I have invested in all the expensive testing and tuning gear for it, and build the motors myself. But I'm just as glad to have this outboard motor be carbureted, and for the reasons already stated.

posted 03-01-2013 06:37 PM ET (US)            

Sooo, the latest. I did not want to chase down things like bad CDI's or rectifiers myself, and the motor was due for it's 800 hour service anyway, so I took this Mercury to the local (if you consider a 30 mile freeway drive local) Yamaha dealer's head mechanic... Tony Johnson, a young but savvy mechanic with a great, pro-customer demeanor. I tried to demonstrate the hard cold-starting for him, but it started right up anywyay. I had run it on the muffs earlier that morning and thought it had cooled off enough to demostrate a hard cold-start. Tony, wise beyond his young years, said he likes to to a leakdown check on just about every motor that's having problems, and I agreed. I should have done a leakdown check myself, but I lent my leakdown tester to a buddy (months ago) and haven't asked for it back, (I've had his engine hoist for more than a year, so I'm not feeling slighted).

Before he did the leakdown test, he fired it up again and closed off the pilot jets one at a time, and when he did the bottom one, it did not stall the motor and had very little effect. So no surprise that Tony found the top three cylinders nice and tight, and the bottom cylinder was leaking about 22 percent through the crank case. That would have made me think it was a worn bottom cylinder and I'd be sunk with despair. But that's the difference with a pro mechanic and a guy like me, even though I have the knowledge and skills to build motors from a pile of parts, that still does not develop diagnostic skills like a pro mechanic. Next, he did a compression check and all four were crackling high, even the bottom one. He knew immediately that it was probably stuck rings from carbon. He stuck a probe in the bottom cylinder and scraped off some carbon and that made him even more sure. He de-carboned the motor, (I did not ask him his technique), and sure enough, the leakdown numbers are up where they should be even for the bottom cylinder. He said it runs MUCH better now, and I didn't have any serious problems with it before other than the hard cold starting.

So maybe the leaky number 4 cylinder (bottom) was it all along?

The 800 hour service also calls for checking and adjusting the valves, so there is even more room for improvement. We'll see.

I'm going to ask him to check resistance in the cables from the battery under the console to the motor. With one battery like I'm running it now, it cranks a little slowly at first and I wonder if that causes a weak spark that makes cold starting harder? I was going to go back to dual batteries, but I didn't want to pay good money for a couple of new ones until I had the motor running satisfactorily... which it looks like we're heading for.

One other thing, he noted that I had the carbs balance up quite nicely with my $99 motorcycle, 4-carb manometer. So I won't be investing in the $1500 vacuumate.

posted 03-03-2013 10:44 AM ET (US)            

Our OMC's (your old v6 and my gaggle of v4's), lack the ability to adjust throttle angles with respect to the others. Those are fixed by design.

There were many high performance cars from the carburetion era, mostly European some American, that had multiple carb setups. A short straight shot from the intake to the cylinders, identical for all cylinders is good. A growing number of modern efi motors are the same way. My wife's modern BMW v8 has eight individual throttles, one for each cylinder, but they are covered by a common plenum.

posted 03-30-2013 12:19 PM ET (US)            

In my last installment, I had the motor in the shop for it's 800 service. They found the leakdown on the bottom cylinder to be too fast, and did a de-carbon treatment, which brought the leakdown up (down) to match the others.

Just got the motor back after several weeks, having told them to take their time, because I was going overseas and then I was sealing cracks in my driveway and just as happy NOT to have my Whaler around and in the way. They finally called me last weekend and asked me to come get it, (they were probably on to me, using them as free storage ;) )

The good news? The bill. $575 out the door including tax, parts, and labor. And that was for a MAJOR service which includes valve adjustment, in a VERY expensive part of the country, in a shop that is in a marina. I was satisfied with that price, pleasantly so.

The interesting news? The carbon. Runs like a top after a thorough de-carboning. That was the only thing the shop could put a string to as to why it runs so well now, and not as well when I brought it in. (Remember, when I brought it in, it was running fine for my uses. A little hard to cold-start and fiddly on some adjustments, but otherwise, nothing that would ruin my day).

Interesting news 1a: The previous owner was religious about using quickleen for his 800+ hours of ownership. I put about 50 hours on it in my two years, leading up to now. For the last two tanks before servicing I didn't use Quickleen. I used Techron. And those two tanks are when I started having non-new-quality running issues. Could it be the Tehcron? Doubt it. I'm _sure_ it would take more than two tanks to carbon up an engine. Further, my running problems started almost as soon as I added the Techron. Carbon definitely doesn't build up instantly. And further still, Techron is a well known and well respected and established product.

Interesting news 1b: So, they de-carboned it, and they said they found a LOT of carbon over all, in all four cylinders, (remember, it was the only bottom cylinder that had the stuck rings though). So what's interesting? After 800+ hours of religious use of Quickleen, it still carboned up.

Thoughts: Maybe that means that even good additives will only slow the buildup, not stop it, and that de-carboning is still necessary periodically for some motors? Recall, that the 50 hours I put on this motor were over the last two years and that 35 of those 50 were probably on the muffs in the driveway, idling.

My conclusion: As with the old Evinrude saw of blaming everything on VRO, don't be too quick to blame everything with this motor on the carbs. I took mine off and cleaned them three times, chasing this problem which turned out to be carbon. BUT, if you're sure it's the carbs, they are not that hard to do, (slow going, but easy work), and you don't need the $1500 Vacuumate balancing tool. The $110 liquid motorcycle manometer from Motion Pro worked just fine for me. Even the professional techs told me I had it balanced just right.

Anyhow, for now, as of my first time out since the de-carbon work and 800 hour service, the motor is running about like new. Easy cold-starting, transparent, turn-the-key-and-go operation, indistinguishable from an EFI four stroke... except we can work on it ourselves.

posted 04-03-2013 03:29 PM ET (US)         

quote:

---

started it and ran it on the muffs in the driveway more or less weekly, certainly no less often than every other week, but mostly weekly. But did NOT take it out in the ocean very often where I could put some load/speed on it, (and I think that is important).

---

Letting two strokes idle in the driveway repeatedly without ever running them hard will cause carbon build up problems.

posted 04-04-2013 05:13 PM ET (US)            

quote:

---

Letting two strokes idle in the driveway repeatedly without ever running them hard will cause carbon build up problems.

If your not going to run it up to temp under load you're better off to leave it be.

---

This motor is a four-stroke-cycle motor. A Mercury 90hp FourStroke. But your point is well taken.

posted 04-26-2013 01:09 AM ET (US)            

Anyhow, I'm very high on this boat/motor combo right now. Especially since I've taken the heads and transfer covers off my Hydrostream's "Frankenstein" v4 crossflow in an attempt to determine it's origin. So my 17 Alert/special service Montauk is my only runner at the lake until I button the v4 back up. Which reminds me... WHOA! Does this 90hp FourStroke ever sip fuel in comparison to my fast, lightweight, but old carbureted two-strokes.

posted 04-30-2013 10:17 AM ET (US)            

Now I'm over 500 hours and haven't ever decarbonized the motor. Nor have had even the slightest carb problem since knocking off the EPA plugs and adjusting the mixtures "properly". The last 3 years, I've settled on Blue Stabil + Quickleen as my witch's brew, and that seems to be the winning combination. I tend to cruise at 3800-4200 pretty con stantly, and wonder sometimes if more variation in engine speed will help longer term to keep things right at other throttle settings. I'll hit WOT for a minute or so every other time out. I know it's the right thing to do for clearing out deposits, but I still have psychological issues with this engine - fear that running it at WOT for more than a minute will shake something loose since the engine is supposedly so "delicate". Not completely rational, and no evidence whatsoever, but always comes to mind.

Moot point anyway as I am on the ocean in Maine and there are few opportunities for running at WOT, particulalry since I am lazy and usually don't go out until the afternoon when it is warmer, but also windier and choppier.

posted 04-30-2013 12:16 PM ET (US)            

I think it was 6-7 hrs total. (Plus one impeller) -- But I was working on the water (boat house), and it beat a day in the office.

One trick I do for balancing and set points of all the carb needles and valves, is before I unscrew items, I screw them in all the way until the stop while counting the turns. (Write it down somewhere, when I put it back together it goes in the same spot/point.) -- Or I etch an alignment mark.

One comment about carb build up, use marine grade oils and products in engines. Marine grade oils have much more detergents in them than automotive types due to regulations. This will also help prevent carb build up.

posted 06-24-2013 12:44 AM ET (US)            

The Whaler did what they do well, give confidence.

But this thread is about the motor. And it acquitted itself magnificently. It might as well have been a brand new EFI four stroke. I'm glad she tolerated the hard 5500+rpm running so well. Not to down on Mercury, but I was feeling reassured about the fact it is a really a Yamaha. That doesn't in the least make me less confident in the new Optimax ProXs I talked about in another thread for another boat.

posted 08-24-2013 06:05 PM ET (US)            

But this thread is about the motor, and the fact that there is nothing so say, says everything. Another day of easy, instant starts, and perfect, stumble-free, "might-as-well-be-EFI", operation. As a point of reference, the great running began for me, after a BIG de-carbon job performed by the Yamaha techs, during the 800 hour scheduled service. Yamaha tech's, because the powerhead is identical to the Yamaha F100. They knew it like the back of their hand.
This motor is so Yamaha, that back when I thought the problem was the carburetors, I rebuilt them with Yamaha carb kits, in Yamaha packaging. Believe it or not, the Yamaha carb kits were actually _cheaper_ than the Mercury-branded carb kits.

posted 11-15-2013 10:57 AM ET (US)            

It has been my opinion that in outboard engine applications the carburetor is just fine. Most of the operation of an outboard is at low elevations and in very moderate temperatures. The carburetor is a wonderful fuel-air mixing device in those conditions. The older outboard engines with electronic fuel injection were mostly very simple open-loop controlled injector systems, and they really did not have anything spectacularly better about them compared to a carburetor, other than they could be controlled electrically. The orifices in a carburetor are probably not much different in size than the ones in a fuel injector. Bad fuel can clog either of them. Too many people over-sell the benefit of simple fuel injection systems on outboard engines.

The most important difference between carburetor fuel systems and electronic injection fuel systems seems to be in the closed fuel system of the electronic systems. The closed fuel system tends to prevent the evaporation of the fuel from the system. Carburetors that are left to sit a long time without use may have the gasoline evaporate, leading to some residue in the system.

On my carburetor engine, I used to prime the fuel system before the boat was put away for temporary storage, to be sure to get the carburetor bowls filled with fuel. I also left the engine in an operating position, to prevent the fuel from spilling or draining from the carburetor bowls. If you leave a carburetor engine stored with it tilted to horizontal, most of the fuel drains from the carburetors.

Using those storage methods, I could depend on my carburetor engine starting up beautifully after many weeks of not running.

Also, I never tried to pull the fuel hose off and let the engine run until dry. That method might work on a pre-mix engine, but not on modern engines that try to automatically mix the oil and gasoline. You just wind up with much too rich oil mixture.

posted 02-25-2014 11:29 PM ET (US)            

Pick up tube on 2005 Merc 6 gallon tank dropped off. Engine runs poorly like that. Could burn it up I think. Second tank worked better.

Screen on bottom looked great, plastic tube attached to that pick up is attached very well, But the tube is just pushed on the top fitting. Plastic expanded and dropped off.

Added a clamp, and it works now. Have to do the other one before it falls off. Just an unending list of surprises.

posted 06-08-2014 02:20 PM ET (US)            

Ever since I got the massive decarbonizing procedure, (the shop said the carbon buildup was extreme), this thing has run like a brand new EFI motor, not the maligned carb motor of it's reputation.

Binks, I'm not sure what you mean by all the effort I'm putting into this. After I figured out what was wrong with it, (extreme carbon buildup in my case), it has run like a top ever since. Utterly reliable and trouble-free, Including after sitting for months and months at a time Yes, it is a four-stroke, but because it's carbureted, you can clean and balance the carbs yourself with an ordinary motorcycle balancing manometer. As a fellow carb guy, you should be able to relate to that. All my other motors are carb two-strokes.

posted 06-12-2014 09:44 AM ET (US)            

Do you run fuel out of yours when parked?

I am very happy to hear from you and some successes.

Maybe I will get this situation behind. Will let you know. I have about one more round of this continum in me. .?

Did you ever find in-line filters at the fuel line carb connection, inside the fuel line.? My mercuy shop manual shows them. Looks lilke entire manifold has to be removed to get at them. That is my current unknown. Do I take the carbs and manifold off to look or just keep on trying.
And then there are the dealers and mechanics., and $,$$$.???

One dealer already told me there are no little in-line filters.

Nice to hear from you!

posted 06-12-2014 10:51 AM ET (US)            

I wouldn't be afraid of pulling the manifold. Its super easy. Not even a 10 minute job.... Less if you are familiar. And it has one of those modern rubberized metal gaskets that you can reuse again and again.

What do you use for balancing? The electronic balancer tool is over $1000. I use a motorcycle manometer from Motion Pro. The pro Yamaha mechanic who decarboned my motor and did the 800 hour service said I had it balanced perfectly.

posted 06-12-2014 01:10 PM ET (US)            

To remove manifolld, do carbs come with it?
Do we need the little in-line filters?

posted 06-12-2014 04:22 PM ET (US)            

https://lh6.googleusercontent.com/-zwYaosP6IsU/Uoa8r-KPj-I/AAAAAAAAFl4/ A3oqHdey9IU/w452-h605-no/IMG_1724.JPG

The aluminum manifold on the left is the part that bolts to the side of the engine block. I don't remember if you have remove the big black plastic plenum from the carbs to get to the bolts that hold the aluminum manifold to the block. Something in my memory tells me you can just remove the whole kit and kaboodle in one shot... something I didn't care about because I thought I needed to disassemble the carbs, when I was taking them off.