Irratic idle, lean sneeze

[guy74]

I've finally torn into my 1989 100XP Evinrude, E100STLCEM, looking for why it doesn't idle right. #4 is running lean at idle, spits once in a while. I can cover the idle air bleed on #4 with my finger and the motor idles perfect. I've rebuilt both carbs, they had nothing wrong with them, perfectly clean. The only thing I've found is a leaking recirculation check-valve, will flow in both directions, on the offending cylinder. The other three check-valves work fine. I visually inspected the reeds though the carb mounting holes with a borescope, nothing looks out of place. My guess is that the check-valve was leaking air back into #4 and leaning out the idle mixture, am I on the right track? BTW compression is 120-122 across all cylinders, with good spark.

 

[guy74]

Re: Irratic idle, lean sneeze

Anyone ever had any experience with this kind of problem? Any other wisdom before I put it back together? My new check-valve should be here today or Monday, so I'll let you all know how it runs when I get it back together.
Goodday,
Brian

 

[reeldutch]

Re: Irratic idle, lean sneeze

could be the trohtle shaft leaking air .

 

[guy74]

Re: Irratic idle, lean sneeze

Thank you for the reply, and thanks to everyone who took time to read my post. If no one has any other ideas, I'm gonna put it back together when I get the parts. BTW the throttle shafts are fine, I rechecked them for play after the suggestion, I don't think there is any problem there.

Thanks again to all,
Brian

 

[reeldutch]

Re: Irratic idle, lean sneeze

even if there is no play and they loook very tight they can still leak a litle air to trow your idle of and make it sneeze.

run the motor and spray with presisiuon carb cleaner on the outside of the trole schaft.
NOT inside the venturi.
if the motor changes behavior you found your leak.

you can try this around the crankcase also.

 

[guy74]

Re: Irratic idle, lean sneeze

I got it put back together this evening, fired it up on the stand. It runs smooth with no sneezing now, so it seems that the check-valve was indeed the problem. Thanks again for taking a look at my post, and reeldutch, thanks for the suggestions.
Thanks,
Brian