Cough at idle

[Copperhead1960]

I have an 87 40hp Johnson twin. I have just rebuilt the vro pump and switched to premix. I have kitted the carbs and have the proper champion plugs. I can not get the engine to run smooth at idle. With the cold start lever half up it will come to speed and cough, then come up to speed and cough over and over again. I then put it down in idle and it will cough and run a time or two before cough and stall. I decarbed the engine yesterday in hopes that it would fix it but runs the same. I advanced the idle spark a half to 3/4 turn and it will idle w/ a cough all day long but too fast.

My son is driving me crazy wanting a boat ride.

 

[karlow1]

Re: Cough at idle

Did you adjust the mixture screws after rebuilding the cabs? It sounds like it's too lean, or the timming is out of whack.

 

[Silvertip]

Re: Cough at idle

Idle mixture and idle speed need to be set with the boat in the water -- not on muffs. Set idle timing where it is supposed to be and fix the carb issue. Cough at idle is a mixture problem.

 

[dajohnson53]

Re: Cough at idle

Can't this be an air leak problem too? The only time I had an idle cough, I found a leaky plug on the VRO pump (which had been converted to premix). WHen I fixed that, the idle improved tremendously and the cough disappeared. Check all your fuel lines very carefully.

 

[Copperhead1960]

Re: Cough at idle

My carburators have fixed jets so I can't adjust mixture.

Is there a easy way to look for leaks in hoses? We work with 2cycle saws at work which often lose their crankshaft seals. The reason I mention it is because our mech. is just dying to dig into it to replace seals...I really don't think that is the prob. Are seals a common problem in outboards?

 

[Silvertip]

Re: Cough at idle

Crank seals are not a "common" problem. It can happen but is not something one sees routinely. Were the jets removed and cleaned when the carbs were rebuilt? Yes -- an air leak can also cause the problem which is essentially a mixture problem. In other words its too lean. To find the cylinder acting up, remove the air box and with the engine running, hold your fingers (first one, then two then three) over each carb intake. When the coughing stops you found the bad cylinder.