1963 Johnson 75 hp running rough

L

lx.crowell

Seaman Apprentice
Joined
Jul 12, 2012
Messages
40
I have a 1963 75 hp johnson with electric shift. the motor has been running a little rough during idle and when you go to plane it out it seems to run on three cylinders and then will smooth out and run smoothly but still won't have all of the top end power that it used to have. When i pull the plugs to do a read on them they read clean and good so i am very confused right now. Also what plugs should you run in that motor as i am currently running j6c's in it. Any help would be greatly appreciated, thank you.
 
Joe Reeves

Joe Reeves

Supreme Mariner
Joined
Feb 24, 2002
Messages
13,262
Re: 1963 Johnson 75 hp running rough

Champion J6C plugs gaped at .030 are okay... J4C & J6C are the recommended plugs.

What are the compression readings of all cylinders?

It may be time to replace the points, condenser, and rotor. If that engine has automotive ignition, the rotor should have a straight squared off tip to its business end... NOT a wide hook like appearance to the business end which is for a magneto distributor.

Point are to be set on the high lobe so that a .020 gauge goes thru but a .022 will not.


Let us know what you find.
 
L

lx.crowell

Seaman Apprentice
Joined
Jul 12, 2012
Messages
40
Re: 1963 Johnson 75 hp running rough

ok I bought the boat three years ago and had a compression rating of 100- 105 and replaced the points last year in the middle of the season and the condensor was replace about 2 years ago. The distributor cap is automotive type.
 
L

lx.crowell

Seaman Apprentice
Joined
Jul 12, 2012
Messages
40
Re: 1963 Johnson 75 hp running rough

I did a compression check this weekend and got 90psi on all four cylinders and ordered new pionts and a condenser but that wont be in for a week or so yet. I had pulled the plugs on it and the plugs were able to jump a 1/4 inch gap, and the plugs from the 1+2 cylinders read lean burn while the 3+4 plugs read rich burn so I think my promblem is fuel and not electrical. Any ideas, thanks in advance.
 
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