Lean sneeze at idle

[guy74]

Hi everyone,
I'm working on a 1989 Evinrude 100 hp V4. It seems to run lean on one cylinder at idle. I have taken the carbs apart and checked to make sure the idle passages were clean. The carbs were rebuilt in 06, according to the previous owner, they were spotless inside. It seems to run lean on number 4 cylinder at idle, if I cover the idle air bleed for that cylinder with my finger it smoothes right out. I'm not sure where to look for the cause of this problem. The motor seems to be in very good shape, good spark on all four, good compression(120,120,119,120).
I'm kinda stumped looking for the cause, I think it must be a vacuum leak, but I'm not sure where the most likely places are to look.
Thanks,
Brian

 

[72SideWinderSS]

Re: Lean sneeze at idle

Places to look:

Lower carb base Gasket.

Confirm air bleed for number 4 is correct size.

Fuel pump takes its pulse from number 4 cylinder. Either a pulse hose or mounted directly to the block.

 

[CharlieB]

Re: Lean sneeze at idle

#4 carb idle FUEL passage (fuel dip tube) is restricted with crud.

 

[Dhadley]

Re: Lean sneeze at idle

Start with the basics. Make sure the cam follower is not touching the roller. Then loosen the screw for the carb linkage and make sure all butterflies are completely shut.

 

[guy74]

Re: Lean sneeze at idle

I finally got the chance to work on it again. Dhadley was right on, the butterflys in the lower carb were slightly open. Did a complete link and sink on it, run much better.
Thanks,
Brian

 

[Dhadley]

Re: Lean sneeze at idle

Thanks for the follow up! It's always good to hear how things turn out.