Low compression in #1

olpace

Cadet
Joined
Aug 28, 2009
Messages
7
I have a 1973 50hp Evinrude. Top cyl has 100psi and the bottom cyl has 130 psi. The motor was left sitting for a long time and had seized up. I was able to get it freed up, but now have low comp in the one cyl.....When I got the motor the head cover was pulled, but not the head. I have replaced coils due to no fire and later found that it was a bad power pack which I will be receiving tom.... The head cover gasket seems to be damaged..... Could this be the cause of my low compression??? Or maybe a stuck ring....? Kind of at a loss on what to do at this point. Any help and/or advice would be much appreciated... Have already rebuilt carbs and replaced fuel pump/lines etc.... Have invested too much money to just give up on it, but dont have the money to rebuild it at this point either..... Many thanks....
 

JB

Honorary Moderator Emeritus
Joined
Mar 25, 2001
Messages
45,907
Re: Low compression in #1

I wouldn't call 100psi low, olpace, but it is outside the +/- 15%.

Most likely cause is some carbon in #1. Do a decarbonization and check it again.

Good luck. :)
 

tashasdaddy

Honorary Moderator Emeritus
Joined
Nov 11, 2005
Messages
51,019
Re: Low compression in #1

agree with JB.
Decarb, take a can of seafoam put 3/4 of it in the gas tank, with only 1 gallon of premixed gas. put the rest in a spray bottle. start the engine, and let it come up to temperature. then remove plugs, and them some real good shot of seafoam into the cylinders, replace plugs, let sit 15 minutes. restart, and spray the rest of the seafoam into the carbs, so the the motor almost stalls, wait and repeat until the seafoam is gone.then take for a wide open spin. then put in new plugs, ad premixed gas to the tank, and take it for a wide open throttle spin. it is going to smoke like a house on fire, during this process.

afterwards compression.recheck
 

kenmyfam

Supreme Mariner
Joined
Aug 10, 2006
Messages
14,392
Re: Low compression in #1

Agree as well. Decarb should help to even things up somewhat. Well worth trying before considering ripping it down.
 

olpace

Cadet
Joined
Aug 28, 2009
Messages
7
Re: Low compression in #1

Thanks to all. I will not have time to work on it again for a couple of weeks, but I will keep everyone posted on the issue.
 
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