120hp johnson loses power and picks up again

[tiftonk9]

My 1988 120hp johnson goes strong sometimes and other times it doesn't. At full throttle I only get around 3000 rpms but after a while it picks up to full speed at around 5500 to 6000 rpms. While running at WOT it sounds as if it is struggling to keep speed. The sound of the motor fluctuates up and down. Just bought boat and compression is good. Not sure about fuel pump.

 

[Solittle]

Re: 120hp johnson loses power and picks up again

What troubleshooting have you done?

Your symptoms point to a need to rebuild the carbs. Get the BRP/OMC shop manual. They are a lot easier to rebuild then their automotive cousins.

I doubt that your problem is with the fuel pump. The rpms would not vary as you describe.

I have a pair of 1987 110s.

 

[tiftonk9]

Re: 120hp johnson loses power and picks up again

I by no means am a mechanic. I have done no trouble shooting because I have no idea what i am doing. I just want to have an idea of what might be wrong so my marine mechanic wont take me to the cleaners. (no offense to any marine mechanics intended but my local mechanic has tried to screw me in the past. the other closest mechanic is over an hour away.)

 

[Walker]

Re: 120hp johnson loses power and picks up again

Also check and clean all the ignition coil grounds.