1983 Johnson 120hp running a little rough sometimes..

[mischmerz]

Howdy -

I am restoring a '83 Aquapsort 200XF with an 120hp Johnson original motor. It still has good compression and starts and runs well. However - I recently noticed the sound changing slightly and dropping about 50 to 75 rpm. It goes from a clear sowing machine sound to something more rough sounding - for some time (variable, 20 to 40 seconds), than back to sowing machine and after a little while back to rough. Increasing throttle always switches to "sowing machine" for a moment, before going into rough again and dropping some rpms. So I suspect carburetors? A friend suggested spark plugs .. what do you think?

Thanks.

Michaela

 

[racerone]

A 120 in 83 ??---------Post the model #

 

[mischmerz]

I am sorry, I was wrong. The motor is 1987, the hull is 1983.

 

[Crosbyman]

have you tried TLC.... decarb? Merc Engine Tuner, tank venting, hoses,... new plugs just in case etc.... maybe a new impeller which is probably a good investment anyway


before tearing into bigger issues ?

 

[racerone]

Possibly loosing spark on one cylinder ?-----Use a timing light to see if that is the fact.------You have to do the work.--- No one can do this for you from 10,000 miles away.

 

[mischmerz]

Thank you I appreciate your advise. I wasn't asking for you guys to do the work, but maybe pointing me in the right direction. No need to to dismantle the cylinder head when the problem is in the drive shaft. In other words - some things are more likely to be the cause of my problem than others. I'll look into it. Thanks again.