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115 hp Johnson runs great until the wakeboarder falls down, then runs like crap

J

JP102

New member
1978 115 hp V4 johnson

At the start of the day, engine starts up, idles nice, performs like a champ. After a while and a couple of kids wakeboarding when I go to idle the engine really chugs and I have a hard time getting it started. While trying to get it started I can see and smell on the water. It eventually starts and I get a whole lot of white/blue smoke and have to get in in gear very quickly or it stalls. Chugs for a bit and then all of a sudden we are off and it runs at WOT no problem; until the kid falls down and we do it all over again. I should note that the first couyple of cycles of WOT to idle and back, the engine works great. As the day goes on, the problem gets worse. This problem has been on and off for a couple of years. I kept putting it off as carbon build up.

Carbs have been cleaned and rebuilt, got good compression all cylinders, good spark on all cylinders. Performed link and sync to the best of my limited abilities and I run seafoam in the gas to prevent too much carb build up.


All thoughts/comments welcome. Anyone think it might be the reed valves?

Thanks!
 
Will spark jump a gap of 7/16" on all cylinders ?? ----that test indicates " good spark " on an outboard like yours.-----------Run it with a timing light and see how spark behaves on all cylinders.
 
Yes spark jumps gap of 7/16" on all cylinders. Are you suggesting running inductive timing light on each of the four spark wires? Do you suspect there will be a difference?
 
You need to do some testing and trouble shooting.-------------------I can not specify a " magic fix " from where I am.
 
If you have good spark and good, even compression, that only leaves you with air/fuel mixture. Sounded like your motor is getting more gas and less air. A ruptured fuel pump diaphragm can cause the saying issue or your motor is having a hung up floater in one or more of the carbs. Do you have an inline gas filter? You should perform the carb cleaning again and adjust the floats tilting upward slightly, install an inline filter. I would never count on the result of the rebuilt carbs, not even by the most experienced mechanic. How old are your primer bulb and fuel pump? Target the fuel problem and you will find either a fuel pump or carb issue.

If you have a heatsoak issue or a misfiring, you wouldn't be able to run at WOT many times like that. Unless, you have a slightly intermittent powerpack.
Good luck.
 
qhn - thanks. The primer bulb is about 3-4 years old, fuel pump a bit newer. I have an inline gas filter, but the problem occurs with or without it. I'm definelty getting too much gas as I can see it on the water and can smell it.
 
QHN - thanks for the direction - problem solved!

On one of the carbs, the throttle plate was only opening 3/4 of the way at WOT. One simple adjustment aligned the two carbs and then engine ran great all weekend.

Thanks again.
 
One more thing you might check are the spark plugs at the end of a day after the motor is cooled off. I do not like your reference to the white smoke which becomes common with a head gasket going bad. If/when you pull the plugs if one or two are clean as a whistle that also indicates a head gasket leak.

Just good stuff to check ;)
 
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