1975 Johnson 115 HP Looses power at Full throttle

[roger]

" Just got a 1975 Johnson 115

" Just got a 1975 Johnson 115 HP
Took it for a test run and she goes pretty good
Revs up nice, but when she catches up at full throttle it starts to dog down and loses power.
I pumped the primer bulb a few times and opened her up again. It ran better for a minute then started to lose it again.
When this occurs you can back off the throttle and she picks up RPM again and keeps on going.
I plan to change the plugs, and water comes out all the right places when I hook up the hose.
Any suggestions? "

 

[joereeves]

"Roger... Always start out tro

"Roger... Always start out trouble shooting by taking a compression check of all cylinders which should be 100+ psi and even on all cylinders, and check the spark with the spark plugs out. The spark should jump a 7/16" gap.

If you're saying that the engine does hit full throttle and stays there for a short time, then starts to die out... that would be most likely due to a fuel/air leak at one of the fuel hose connections, the plastic snap on fuel connector has a leaking "O" Ring, or if you have a built in tank... a sticking "Anti Siphon Valve". That type valve is located at the tank where the fuel hose connects. It would be about 2" long, aluminum, and would contain a ball, seat, and spring. if it exists, knock out the inner parts and reinstall it.

If however you're saying that the engine starts to die out when you get near full throttle, I would suspect that the carburetors are fouled and will require cleaning and rebuilding.

If none of the above problems exist, it's always possible that you have a failing fuel pump, but usually when a f/pump fails, the engine fails to run at any speed. What happens if you have someone constantly pumping the fuel primer bulb? Does this problem still exist?

Joe

"