1985 johnson 90 idling problems

[baltra]

I just read all posts relating to johnson 90 1980-89 and idling problems and could not find an answer for my problem. My engine is sputtering at irregular intervals when idling only. Powerhead had just been rebuilt, compression is 115-120 on all. I have checked spark on all 4 cylinders, appears to be good, just a couple of times I thought I saw missing spark on 2 cylinders, but it was ok all other times, I did several spark tests! Last time in the water, coming back from the reef it would run on 3 cylinders only, then I "touched and moved" all coil/pack/ cables and it was ok. Still at idling, it sputters and eventually dies.
One of the packs' leads-to-coil is in not great shape, boot is cracked and spark jumped, but I isolated with extra rubber tape and stuff.
Carbs were cleaned with powerhead rebuilt.
What could be causing the intermittent misfire?

 

[boobie]

Re: 1985 johnson 90 idling problems

Get a timing lite, run the boat when it acts up and check all the cylinders by looking into the lite and look for black spots. This will tell you which cyl's are acting up. It's a place to start.

 

[69stingray]

Re: 1985 johnson 90 idling problems

You might want to check the four check valves on the intake. If the check valves are bad it will create a lean condition and a rough idle and
or (lean sneeze).

 

[emdsapmgr]

Re: 1985 johnson 90 idling problems

Check your spark as Boobie mentioned. After you confirm you have good spark on all 4 cyls at idle, then it could be a carb issue. If the idle passages in the carbs are not perfectly clean, the engine will occasionally randomly misfire at idle. Called a "lean sneeze.) Usually this will clear up as soon as you open the carb butterflys slightly-but will return back at idle. If this is your condition, pull the carbs apart and clean the idle passages again. A low idle can also cause problems. Your idle needs to be set at 650 rpm's, when the boat is floating normally in the water and the engine is in forward gear.