[Jacbo]

I've had this '86 merc 8hp for a while now and it's always ran the same way... crappy. It's always reliable and starts easily but it doesn't like to idle. Sometimes you can get it to idle but if you run it in the higher rpms it will almost always die when you return to idle speed. It acts like it's leaning out in the low rpms but performs flawlessly at WOT. The carb is a single jet w/o the separate low speed/high speed adjustments like some of the older OMCs. I put a carb kit in it/cleaned the carb and it did not change a thing. Just did a compression test on it and it's reading 90lbs and right under 90lbs. Not the best numbers I've seen but fine for an older motor with some hours.

The only other thing I can think of would be the reeds. I'm gonna tear down the carb one more time and put everything back to factory settings and see what happens. If that doesn't work boyesen power reeds for this motor are only $30. Has anyone had problems with reeds before? Any insight, tricks to try first?

 

[Brett]

24 year old motor, 90 psi is workable, especially for a 2 stroke.

I'd check my idle settings (rpm's) with the boat in the water, in forward gear.
Low idle rpms will stall out your engine. Memory says 650-750 rpm is about right.
Setting idle rpm's on a hose flush or in a bucket won't fit on water conditions.

 

[Jacbo]

I have the idle adjustment cranked up pretty high to compensate for the real problem. When it idles correctly it idles at over 1000, otherwise it starts to idle at probably about 750 and then sputters out and dies. Now it's coughing even on the leanest adjustment it will run on, I've usually had problems with coughing due to the fuel adjustment being too rich.

 

[Brett]

Sounds like you've tried the right things.
I agree, do the carb rebuild again, verify no air leaks
and that all the carb passageways are clean.
Reset to factory specs, including timing.


I had one engine I could never get to idle right.
not even a carb rebuild worked. Replaced the carb and it ran great.
As I had replaced the carb, I took the old one completely apart down to the last piece.
I found some of the tiniest passageways were completely blocked with metal fragments.
Solvent won't work on metal shavings. Never found where the metal came from.

 

[Jacbo]

Ok two questions.

1. How do you time a two stroke?
I've always thought about doing this but never really figured it out.

2. Can someone with a mercury 6-15 hp tow stroke tell me if the actual point of the fuel mixture adjustment screw is supposed to be sharp or rounded?
Mine is a rounded point but other outboards I've dealt with (omc's) had almost needle sharp points on the lean/rich adjustment screw.

 

[Frank_Sebastian]

For an older small engine the carburetor should be an easy fix. Anyway check out this site and see if you might have missed something.

http://www.marineenginedigest.com/diy/carb.htm

On larger engines wasps or worse muddobbers will build a nest in them. I doubt you have that though. Anyway sure that the o ring around the needle valve is good.

Best regards,
Frank _S

 

[Brett]

Obtain a OEM shop manual for your outboard model.
In it you'll find complete instructions and specifications for timing your engine.
Including pictures of the procedure and the tools needed.

 

[aflatsnut]

Sounds like the carb to me. When cleaning a carb pay particular attention to the tiny holes in the carb body. Run a small piece of wire through each hole then blow out with air. If the carb was gummy the first time you cleaned it you may have to soak it overnight in carb cleaner then do the small holes. These small holes have much to do with the way an engine idles. be very thorough with your cleaning