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Author Topic:   2003 Mercury 90-HP 2-stroke Smokes Heavily
Jim D posted 05-04-2003 11:08 PM ET (US)   Profile for Jim D   Send Email to Jim D  
Last month I purchased a 2003 Boston Whaler Montauk 170 with a 90HP Mercury outboard, 2 cycle.
Since I took delivery of the boat, the engine smokes A LOT at startup and runs very rough. (It smokes the way my inboards smoke after winter layup.) I have to rev it to 2000rpm to keep from stalling until it gets warm. The engine runs very rough at slow speed to the point where the bow rail and VHF antenna shake.
The dealer tells me this is normal for a 2 cycle outboard and it will get better after the 10 hour breakin. I'm not so sure since I have run it at least 5 hours already with no change. The boat does run great at cruise speed.
Can anyone advise me if this is normal? My experience is really with inboards and I'm not sure if the dealer is feeding me a line or not.

LabRtvr posted 05-05-2003 06:32 AM ET (US)     Profile for LabRtvr    
I also have a M170 90 2s bought 1/16/03. With the extra oil for break in and the extra cold water temp this winter I could not even keep my motor runnung at idle when the motor was warm. The dealer leaned it up some to get though the winter. Now with no extra oil and warmer water temp I still get some smoking at start up but it idles and runs great otherwise. Somewhere around 1200 rpms the bow rails and console shake but I just change rpm's. Enjoy!!
1stwhaler posted 05-11-2003 05:10 PM ET (US)     Profile for 1stwhaler  Send Email to 1stwhaler     
I have about 40 to 50 hours on mine and I am told it is the motor design that makes it run rough up to 2000 rpms, it runs on 2 cylinders until 2000rpms,have not found any info on motor that states this (2+1).Also when I trim the motor all the way up I am getting gas and oil residue plus new oil dripping into the motor well,anybody else have this problem,it is not comming from the oil reservor cap.other than tis it runs great and love the 170.
LabRtvr posted 05-11-2003 08:02 PM ET (US)     Profile for LabRtvr    
Now with 20 some hours my 2 stroke it is running good--I idled around the no wake zone this morn casting for gray trout and it did great. I wanted to get out of the inlet into the Atlantic to open up the throttle but fog and the dredge precluded that. My limited understanding is that the Merc 902S does NOT idle on 2 cyl but rather is in need of a carb adjust/alignment when running rough below 2000.
Jim D posted 05-12-2003 07:36 PM ET (US)     Profile for Jim D  Send Email to Jim D     
1stwhaler - yes, the same thing happens on mine. I get oil in the motor well. Didn't think much of it until I read your post. I thought maybe I overfilled the oil reservoir or forgot to tighten the cap.
dgp posted 05-12-2003 07:50 PM ET (US)     Profile for dgp  Send Email to dgp     
et al, welcome to the world of the modern 2 stoke. At some service interval your dealer is supposed to adjust your carbs. I'm talking air/fuel ratio adjustment and carb syncronization with a slack-tube manometer.
jimh posted 05-12-2003 10:43 PM ET (US)     Profile for jimh  Send Email to jimh     
You ought to read over the user manual for the 90-HP Mercury 2-stroke outboard and see if it mentions anything about increased oiling during a break-in period. It may be that the fuel/oil ratio is set initially to a lower ratio to help the engine during its first few hours of use.

There ought to be some information in the manual about this. Perhaps they set a 25:1 fuel/oil for break in and this accounts for the heavy smoke you see.

I also don't think the 90-HP engine changes the mixture automatically. See what your manual says about that. You may have to take the cowling off and move something mechanical to a new setting.

Many outboard motors with carburetors will leak some fuel from the carburetor bowls when they are tilted in the full up position. I have a small 5-HP engine that does this, too. It is fairly common with carburetors that are tilted 90-degrees from their operating position.

There used to be a practice of pulling off the fuel hose feed and letting the engine run so that all the fuel in the carburetor bowls would be used up. I don't know if Mercury recommends this or not. It is another answer you can probably find in your owner's manual.

I don't recall the 3-cylinder Mercury outboards having a shut-off of one cylinder for idle operation. I think the 4-cylinder engines, like the 115-HP model, have an approach like that. They shut down 2 cylinders at lower speeds.

jimh posted 05-12-2003 10:48 PM ET (US)     Profile for jimh  Send Email to jimh     
[Changed TOPIC; was "Is this normal?"]
FISHNFF posted 05-13-2003 02:04 AM ET (US)     Profile for FISHNFF  Send Email to FISHNFF     
1stwhaler and Jin D,
My 1996 Merc 75 (same as 90) 2 stroke leaked, or should I say seeped oil fron the oil fil cap. Not sure about new ones, but my design was horrible. You would tighten a yellow cap whick would compress a black O ring outward to seal the oil fill neck. I changed the O ring, then the entire cap assembly. I believe the plastic filler neck warped, or distorted. It was fine new, but developed this problem over two years. I would come back to the mooring to find a huge oil slick around my boat. I would find blue oil in my motor well, and upon opening the cowl, find oil saturating my foam insulation.
I was going to buy a new oil tank, but I just sold it cheap and bought a 90 4 stroke. My Yamaha internal oil tank never leaked, and that design was a pop in plug.


Jimm posted 05-13-2003 09:03 AM ET (US)     Profile for Jimm    
Jimh, The Merc manual recomends that a 50:1 oill mix be used in the first tank of gas. My dealer put a 50:1 mix in both 6 gallon tanks. After that no adjustment is needed or available. Mine smokes a bit at start up, but after that smoothes out except for that rail shake at 1200/1500 RPM. Personally, I like the engine...Jim
lhg posted 05-13-2003 02:23 PM ET (US)     Profile for lhg    
Search the Forum for previous discussion from Clark Roberts on eliminating this problem. It has to do with carb adjustments, I believe.

Normally, it is a very smooth running engine.

Salmon Tub posted 05-13-2003 07:22 PM ET (US)     Profile for Salmon Tub  Send Email to Salmon Tub     
I have the a similar situation with my Nissan. At least with the rails vibrating. The engine runs smooth, as long as smooth means rythem of the RPM's, meaning, they don't lop, or skip, or vary, but I do have the shaking rails at about 1200 rpm, at idle, out of gear, the windshield vibrates, and if accelerating slowly, or trolling at various speeds, the engine will go from a lazy vibration, to a faster deep vibration, to a fast shallow vibration, to finally rock solid and smooth at about 1700 rpm and up. Sound familiar? After lots of research and trial and error, here is how I understand the situation. The vibration of a carbed 2 stroke engine at low rpm is first directly related with the amount of cylinders in the engine. So a 2 cyl. will be twice as smooth as a 1 cyl., a 3 cyl. will be more smooth, a 4 cyl. even more, and so on. Design is the next factor. Inlines seem to shake a bit more than v blocks, and with four or more cylinders you can stagger the firing order such as 4,1,3,2 as opposed to 1,2,3 or 1,2. Motor mounts, and even the type of steering system also make a difference. The Teleflex no-feedback system is good because it dampens the vibration at the wheel, but does allow the engine to shake a bit more. Stiff mounts reduce visible engine vibration, but will cause the vibration to telegraph through the hull a bit more (shaking rails and windshield...) But this is nothing that can be changed. The only thing you can change is the timing (within specs.) and to a certain degree, the mixture (pilot screws). I have tinkered around with this alot on my engine and have learned one thing, these adjustments are static, so to speak. What I mean is this: As I recall, my manual calls for a timing of 5* ATDC at idle, and 20* BTDC at WOT. Also the pilots should be set to 1.25 to 1.75 +.125 turns open for cold starts. So, if I set the timing as called for and lean up the pilots a bit, the engine might run smoother at 800 rpm, but a bit rougher at 1000, then smooth out again. If I richen them up, it may now run smooth at 900 rpm, a bit rougher at 1100, and so on. Get the picture? I have had many a time where I set the engine so that it purrs at trolling speed at 700 rpm, only to do the jig in the 5 mph zone at 1000, and then vice verca. None of this shaking does any damage, but it does get annoying. The fact that I have 3 carbs makes it that much more difficult as it throws another factor into the equation. As a general rule, carbs have always had this characteristic, even in cars, they were designed to operate best at a certain RPM range, WOT or cruise, or idle, rather than throughout the whole spectrum. That is where EFI comes in.

I had the leaking oil problem with a 40 hp when tilted all the way up, but that was because the gasket to the oil level sensor had dried up and leaked.

jimh posted 05-14-2003 01:53 PM ET (US)     Profile for jimh  Send Email to jimh     
The tendency for the bow railing on the 170-MONTAUK to shake and vibrate has been reported by a number of owners.

I don't think that it is a function of the engine, although certainly an engine whose vibration period is in sympathy with the bow rail's could cause it to be more severe.

newt posted 05-14-2003 05:02 PM ET (US)     Profile for newt  Send Email to newt     
I have a 2003 Mercury 2 stroke on my Montauk also (not a "post-classic" though), and have experienced the bow rail rattle and the oil leakage.

At just above idle speed, the engine vibration must resonate with the bow rail because the rattle is pronounced. This year, I will stick some toothpicks or slivers of plastic milk carton into the spaces between the rail and the supports - as suggested to me in another thread last year.

The initial break in call for double oil. Your first tank should have been mixed 50:1 so that combined with the autolube you get double oil.

So...smoke during break-in and rattling bowrails means you are not alone.

Jimh, I think you meant "harmony". Don't worry, I can sypathize with that. :)

jimh posted 05-15-2003 12:19 AM ET (US)     Profile for jimh  Send Email to jimh     
No, I meant "sympathy" as in sympathetic vibration. Sympathetic vibration is a vibration produced in one body by the vibrations of exactly the same period in a neighboring body.

This is the process by which the vibration of the engine induces the railing to vibrate.

Swellmonster posted 05-19-2003 05:15 PM ET (US)     Profile for Swellmonster  Send Email to Swellmonster     
If it aint smok'en, its broken!
lakelab posted 05-20-2003 04:49 PM ET (US)     Profile for lakelab  Send Email to lakelab     
Ihave a m-170 as well with the merc 90 2 stroke.It smoked quite a bit during the initial break in and then a few hours after that. Over time it has gotten better. The bow rail vibrates as well at low rpm but just change the rpm a little will usually dampen the vibrations. I found that if I did not fill the opil resevoir up past the bottom of the neck and made sure the oil fill cap was snug then I didn't get any oil leak into the well. The owner manual says something about making sure the engine isnt trimmed down too much as this will cover a port that can cause the engine to run rough. Had problems initially after start and at idle (in marina) but by following Mercs suggestion seemed to cure that problem. Now have about 50 hours on 2003 boat/engine and it just seems to get better.

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