1982 Johnson 15hp WOT issue

[Captain11]

Hello all,

I have a 1982 Johnson 15 hp tiller, pull start.

Runs Great until I try to go full speed. RPM/speed will be good for 5-20 seconds then it will slow down to about 3/4. it then surges slightly but ultimately stays around that 3/4 speed.

I tried to see if it was a fuel pump delivery issue by squeezing primer ball while running but NO change to ailment.

Interestingly, when it is having the issue, if I pull out the choke out slightly it will go full speed/RPM and run great as long as I have it choked. When I put choke back in it runs ok for 5-20 seconds then slows down to 3/4 speed and slightly surges again.

My question is could this be a linkage issue? or a fuel delivery issue? I don't want to "throw parts" at it but I want to see if it could be something simple before I deep dive into repairs.

Thank You Very Much

 

[flyingscott]

Clean and rebuild the carb could be a plugged high speed jet.

 

[Captain11]

Scott, Thanks for the immediate response!

That was my first suspicion, but what confused me is that if it is plugged wouldn't it stop it from going Full Throttle at all? it runs ok for 5-20 seconds then drops to that consistent 3/4 speed with intermittent small surges

I ran some Marine Stabil 360 in the gas mix (idle and WOT for a an hour or two) on Sunday to see if it would break down / clean out something if it was stuck in there.

 

[Captain11]

Cleaned and rebuilt carb. I am having trouble with adjusting the carb and idle speed. It has trouble chugging and slows to the point of stall unless the idle speed is maxed out. Even a quarter or half turn of the idle knob does this. I would like to slow the idle speed so that shifting won't be so harsh. Any tips?

 

[oldboat1]

Start over with the needle adjustment -- 1 to 1 1/2 open from lightly seated. Start the motor and let it warm up at wherever it wants to idle. Adjust the needle in 1/8 turn increments clockwise (leaner), pausing between adjustments. rpms will increase, so throttle the motor down and continue carb adjustments until the motor idles smoothly and shifts without stalling. It too lean it will lean sneeze or stall -- back it out about 1/4 turn.

Think you might be confusing idle speed (throttle) with carb adjustment (air/fuel mix).

 

[Captain11]

Thank so for that. I was not confusing the two. The motor would slow to a stall and not run if idle speed decreased in any capacity.

I have since adjusted the carb like you said. I did this at high idle (fast RPM) and got it running as smooth as I've ever seen it. I was able to slow down the idle speed after and it stayed running smoothly but shutters slightly (I'm assuming it's normal?).

It seems as if It was running too rich before and that is what was causing the issue with the idle speed. Thank you very much for the advice!

We will see tomorrow how it operates at WOT as I was doing these initial adjustments in a trash can... there was a decent amount of buildup on the high speed jet, float and bowl.

 

[oldboat1]

sounds like progress! Not sure about the shudder -- could be a "stumble" (too rich), or a hesitation from too lean(!). Or something else entirely....

(some art to it, on my view). Let us know how it works out on the water.

 

[arctic_dan]

I'm having the same problem Captain11. If you figure it out send me a message.

 

[Captain11]

She Was operating as designed at WOT this weekend. Very Happy for that! The high speed jet and float/bowl was gummed up and a thorough cleaning and rebuild seems to have resolved that particular issue.
The only other thing I noticed is that there was sometimes gas/oil droplets on the water, I had to increase idle speed (side knob) to keep it running at first. I noticed this on startup and idle. Is this normal or is it getting too much fuel?
I'm assuming I'll have to do the full carb adjust again on the lake as I did it initially In the driveway in a trash can filled with water.

Thanks a ton!

 

[tomhath]

A two cycle motor will always spit some unburned oil out the exhaust,

 

[oldboat1]

On my '83 9.9, I usually set the carb needle 1/4 turn richer for cold starting and warmup, then return to leaner setting.

 

[Captain11]

I will try that next time I go out. That would make sense to help resolve the rich condition. Some of these motors just seem have their special "things" we have to do to keep em happy.

Now only if I can figure out my 30hp Evinrude I'd be all set. But I'm afraid that one will require MacGyver, Al Borland, and a witch doctor to fix.

Thanks a lot!

 

[oldboat1]

Yeah, a little more running and a little more tweaking.

Run a thread on the 30hp. (gaffers tape holds a little better than duct tape, in my experience....)