My 25 hp Merc is running rough.

[Jethro]

My 2002 25 hp merc is basically running rough @ slower speeds, chugging and putting out more smoke than usual.
When I checked the plugs they both looked significantly different.
The top cyl. plug electrode looks more "sooty" than the bottom.
I changed the plugs, ran her for an hour and it started again.
What could be the problem?
It's new fuel, oil and plugs.
Thanks

[mallardtone-man]

Tonga may be able to give ya an idea. Other than than, I have no idea.





James

[steve ypsi]

depends how much you have run it but both plugs should run tan with no soot or oily, any thing can cause the oily or sooty condition but one thing for sure its running rich, my two Johnson 70 hp's from the factory, one was burning right even after trolling on Erie for hours and the run back in would clean any oily stuff up if there was any because i never checked it on the water after trolling as that would be to hard, the other I just used to run back in from Erie was burning oily even though it was run at high speed only, since I didn't have a factory manual I counted the turns in on the air screw of the one that was running right by turning it all the way in but don't ever turn these screws in tight, just to where they snug up lightly then back out and I set the other one with the same amount of turns, now the other one that was burning oily is burning right and can troll also because it is burning right.
If you are not familiar with air adjusments take it in and have it done, if to much air gets in it can burn pistons or seize the engine. better to rich than to lean.
If you want to do it yourself turn the air screw in very slow counting the turns as you go until it touchs bottom, then when you come back out add one turn because this will give it a little moire air,
turning screw in is less air and more gas.
If you are not familar with two strokes or mechanic's of a carb have it done by some one that knows how, don't seize a 2500 dollar engine trying to save 50.00I always check the plugs after being run hard for a while to see if they are burning tan, when I make a adjustment I listen to the engine, if its really screaming at top end I slow it down, that means it is to lean.
the first 2 stroke I ever adjusted I knew nothing about the air and gas mixture, it was a 50 cc moped in the 60's, well I adjusted the air screw until it was idleing fast and then ran it, about 3 minutes and it seized the piston by running to lean.

[kroppe]

Smoke means incomplete combustion. Incomplete combusion either means the right amount of fuel, with poor spark/ignition, or too much fuel.

For poor spark and ignition, change plugs and wires, and see if you can test your coil and remainder of ignition system.

For too much fuel, this is likely a carb problem. Either fiddle with it according to your comfort level/abilities or take it in for service. Since you replaced plugs and it was a temporary improvement, my guess is you have a fueling problem, which is probably related to the carb.

[Jethro]

I took the plugs to a shop on Jefferson and the tech. there said that the bottom cyl. was getting flooded?
He said the "sooty" plug was ok.
I accually thought the clean plug looked like a normal burn :confused:
Anyways-I know nothing about outboard repair so I'm gunna take her in next week.
Thanks for the replys, guys :)

[kroppe]

Jethro,

If it's a 2 barrel carburetor, sounds like the barrel which feeds the bottom cylinder may need adjustment. If it's a single barrel, then there may be some kind of distribution problem between the two cylinders.