Can you help interpret these compression numbers

[BillaVista]

1979 Johnson 55 inline 2-cylinder 2-stroke.

Upper cylinder: 132 psi / 145 psi after a couple of squirts of oil

Lower cylinder: 110 psi / 120 psi after a couple of squirts of oil

Seems to me that there's a good chance the rings on both are worn and/or the cylinders / pistons are scored.

Questions:

1) Could this be the cause of my poor idle (stumbles and drops a few hundred rpm), stalling when going into gear, and hard to start if not dead cold or thoroughly warm?

2) Is there any point doing a carb rebuild / link and sync before correcting this?

3) What are the chances it's just the rings that need replacing (and not a piston replacement and cylinder bore required)?

Thanks

 

[milliesdad]

Re: Can you help interpret these compression numbers

It won't hurt anything to do a decarb. Probably the least expensive and time consiumin of all the alternatives. Not to mention a good way to start.

 

[boobie]

Re: Can you help interpret these compression numbers

Do a good decarb first and if that doesn't help, pull the head and take a look.

 

[steelespike]

Re: Can you help interpret these compression numbers

Could be worn but you could try as decarb treatment ,
removing carbon with a product like SeaFoam.
Just follow the directions.
I believe you could also remove the Exhaust cover and examine the bore and a portion of the piston through the exhaust ports.
Sometimes you can look into the spark plug hole.

 

[BillaVista]

Re: Can you help interpret these compression numbers

By "decarb" do you mean pulling the head and removing carbon from the top of the pistons or something else?

Thanks

 

[BillaVista]

Re: Can you help interpret these compression numbers

OK, I think I see what you mean - you mean to use a product like "Sea Foam" that is added to the gas, correct?

How much treated gas needs to be run through the engine to see results (I have a 12 Gallon tank)?

 

[Daviet]

Re: Can you help interpret these compression numbers

Take a look at this post from the "Top Secret File" at the top of the page, maybe it will help.
http://forums.iboats.com/johnson-evinrude-outboards/decarb-394851.html#post2648076

 

[BillaVista]

Re: Can you help interpret these compression numbers

Take a look at this post from the "Top Secret File" at the top of the page, maybe it will help.
http://forums.iboats.com/johnson-evinrude-outboards/decarb-394851.html#post2648076

Ahh - I understand now - thanks!