compression on johnson 20

[larryg]

wanted to know what the compression should be on a 1985 johnson 20 j20crcos.i rented one at advanced and i cnt screw it all the way down,i am only getting 60 on both.i pulled like hell on both.lol

 

[dkonrai]

Re: compression on johnson 20

i have a couple of smaller 3hp, and i have 90 pounds in both motors. have you tried to use a drill with a socket adapter on the flywheel? saves your arms from pulling

 

[AlTn]

Re: compression on johnson 20

could you screw the gauge in far enough to tighen up on the rubber o-ring?...were both plugs out while you were testing?..if not and the head gasket is blown between the 2 cylinders, the cylinders may show exactly equal compression when, in fact, one is say 90 and the other 30..usually about 5 pulls will bring the reading up to as high as it's gonna read, in my experience.If that 60lb. is good for both cylinders, buy a spark gauge <open air gap type> set it at 7/16" and test the spark on both cylinders....the air gap tool is $10 or so..advance should have them....60 lbs is about as low as you want to go with compression....get the motor running, decarb it, and test the comprssion again..it should come up some..

 

[ultra353]

Re: compression on johnson 20

Just for reference my `69 johnson 20 gets 125lbs on each cyl in about 3 pulls

 

[JB]

Re: compression on johnson 20

Go to the Top Secret File at the top of this forum. Do the test described there.

What other people get is irrelevant. 60psi on both is fine on a rope start engine.