85 johnson 120hp low rpm problem

[mwolfey_ky]

This motor sounds great from about 1/2 throttle up to WOT. From 1/2 throttle down it is rough and almost sounds like it is missing. If I go from idle to WOT there is a sizable delay and then it takes off with plenty of power. One piston was just replaced and all new rings installed on others. This only occurs under load. Backed into water and throttle response is instant when throttling on the motor and out of gear. Any thoughts?

 

[Dhadley]

Re: 85 johnson 120hp low rpm problem

We'll assume the carbs are clean if the motor was just rebuilt since cleaning the carbs is part of a rebuild. So, I'd start with compression.

 

[mwolfey_ky]

Re: 85 johnson 120hp low rpm problem

carbs cleaned and good compression

 

[Dhadley]

Re: 85 johnson 120hp low rpm problem

Are you running with the airbox cover on or off?

 

[mwolfey_ky]

Re: 85 johnson 120hp low rpm problem

Everything is put back together.

 

[mwolfey_ky]

Re: 85 johnson 120hp low rpm problem

Does this motor have quick start feature? I read that it needs disabled before setting the timing?

Thanks.

 

[kenmyfam]

Re: 85 johnson 120hp low rpm problem

If I go from idle to WOT there is a sizable delay and then it takes off with plenty of power. One piston was just replaced and all new rings installed

What kind of weight are you pushing ??? Is this a new problem ??? Why was the piston replaced ???
Agree with a compression check to begin with.
Post results.

 

[mwolfey_ky]

Re: 85 johnson 120hp low rpm problem

Pushing under 1000lbs. Don't think weight is the problem. While waiting for this one to be rebuilt we put on a 1983 115 evinrude and the boat popped right up. Piston was replaced because it threw a ring and had low compression. While we had it apart, replaced the other rings as well. Planning to check compression tomorrow. Assuming the compressions are in line, do you think this is a timing issue?