Johnson 20 lean sneeze ONLY during deceleration

[Farris]

I have a 1990 Johnson 20 hp motor running reliably, but I am having a lean sneezing problem. It NEVER sneezes at idle, and it never sneezes at wide open throttle. It only sneezes when I am letting off the throttle to slow down after having run wide open for a few seconds or minutes. During this deceleration, it keeps sneezing every couple seconds until I get it all the way back down to idle. Does this mean I have a bad lower crankshaft seal? If so, how complicated is that to replace, and how do you know that it is the lower seal, not the upper? Thanks for all your help! P.S. I should mention that the slow speed adjustment needle does NOT take care of this problem. It eliminates sneezing at idle, but does not eliminate sneezing during deceleration.

-Farris

 

[johnny 30]

Re: Johnson 20 lean sneeze ONLY during deceleration

had a similar problem with a 30hp,I was told I had a air leak some where,looked everything over and couldn't find one anywhere.I so I decided to look at the timing instead.Took the carb off,cleaned and rebuilt,used Joe Reeves timing procedure(found here on iboats).Did a link and sync to omc specs,fired the motor up and adjusted the slow speed adjustment.It cleaned the problem right up,hopefully that may be your problem as well.

 

[Shorebum]

Re: Johnson 20 lean sneeze ONLY during deceleration

I agree with previous post. Do the simple first. I was getting the spark knock on deceleration between 2500 and 4000 rpm. Remember motor is leaned out as soon as you cut the throttle (no more than idle mixture flowing) and you have gone from way advanced timing to retarded timing at idle. I noticed that this problem all but disappeared after getting my idle mixtures corrected. Hope your problem is this simple.

 

[Farris]

Re: Johnson 20 lean sneeze ONLY during deceleration

Thanks for the tips. Correct me if I'm wrong, but I don't think my engine has adjustable timing. It is a 1990 20hp J20CRESB. I think my Clymer's manual indicates this. Let me know if that seems wrong to you guys.

 

[jonesg]

Re: Johnson 20 lean sneeze ONLY during deceleration

Never heard of a non adjustable timing except a capacitive discharge ignition I had on a chainsaw engine from japan. I suppose it could be though.

One thing I do know is the after mkt manuals are not the best source of info.
Get one of the factory service manuals.
www.outboardbooks.com

 

[Farris]

Re: Johnson 20 lean sneeze ONLY during deceleration

Thanks for the advice. I have ordered a factory manual.