1980 Johnson 75hp

[Finznfeathers]

Ok i'm at my wits end. I bought this boat from a friend and he said the motor needed a new water pump. I replaced the pump rebuilt the carbs and replaced the fuel lines, spark plugs wires.

When I make my first run of the day it runs great, after I come to a stop from the first run it will not get back on plane. The motor sounds like it wants to go but it stalls out at 2500 rpm, if I can get it past 2500 rpm it will take off again. I have rebuilt the carbs twice and tried multiple jets. I put an electric fuel pump on it thinking. Maybe it was starving but its not. The only thing I can think of next is timing. It has 120 pounds of compression warm. It is not overheating either.

Why will itw get on plane when its cold but not when its warm?

Any help would be greatly appreciated!

 

[racerone]

If you have " rebuilt " the carbs twice then maybe it is not a fuel problem !!------Any sign of water on your sparkplugs ??-----Could well be water leaking into the engine from bad gaskets / warped plates on the exhaust covers.----------Does spark jump a gap of 7/16" or more on the 3 leads , yes or no.

 

[9758JB]

Those 75s are known to have electrical gremlins with the ignition systems. My bet is it has something to do with that. I'd check all coils, powers pack, ect.

 

[Finznfeathers]

There is no water on the plugs and the spark will jump a 7/16 gap. When I go to full throttle it almost sounds like I hit a rev limiter but this only happens after the engine is warm. Do these engines have an over heat switch?

 

[racerone]

They have an overheat warning horn.----But it does not shut down the engine.----The boat operator needs to shut the engine off in case of overheat warning !----I do not believe 1980 models came from the factory with a rev limiter.----It sounds to me that it is running on 2 of 3 cylinders.----Perhaps check the flywheel key too.----Should not be hard to figure out what is wrong on these simple motors..