20 hp Coughing

NathanY

Commander
Joined
Mar 16, 2002
Messages
2,408
My 1974 20 Hp Merc is coughing on idle, does not do it when you wrap it up, just at idle, and idles rough. I can not find an idle adjustment screw, but the manual does show one, and I can not find a fuel mix screw although the my manual shows one of those too.
 

NathanY

Commander
Joined
Mar 16, 2002
Messages
2,408
Re: 20 hp Coughing

Yep that looks like my carb. See where it says that there is a fuel mixture screw and a idle screw? Mine does not have one or I am not seeing it. I let it run for about 20 minutes on muffs. as long as I have the choke 95% open it runs fine. But Dont think that would be closed enough to matter. I am going to take it out tomorrow and run the dog out of it. I has been sitting for 10 years. Carb has been rebuilt.
 

12Footer

Fleet Admiral
Joined
Mar 25, 2001
Messages
8,217
Re: 20 hp Coughing

Sneezing is probably not caused by a carb problem. And here is somethuing to consider...the carb was fine before exactly where it's adjustment is now. I would suspect the plugs, ignition, or small amounts of water injestion.<br />Pull the plugs.If one or both are spotlessly clean, it may be water injestion. If they are nasty, replace them.<br />Plugs on the 2 cycle outboard do not hold-up long, and many manuals sugest replacement around the '80hours of operation' mark.
 

Walker

Captain
Joined
Jun 15, 2002
Messages
3,085
Re: 20 hp Coughing

I beg to differ. Sneezing is usually caused by a too lean condition. If you carbs doesn't have a mixture adjustment then you need to give the carb a good cleaning paying special attention to the idle jets.
 

NathanY

Commander
Joined
Mar 16, 2002
Messages
2,408
Re: 20 hp Coughing

I just relplaced the plugs with Champion L78V. The old plugs where not right, they had J electrodes on them, but they did not look bad at all. Both plugs are firing, a beautiful blue flame.
 
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