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I've seen a lot of factory shop manuals, ansd don't ever recall seeing any compression numbers, likely BC of variability in individual samples. Most mechanics have a pretty good idea of where a specific motor should be from experience. The more important criteria is cylinder to cylinder variation. 50 psi is fine for a pull start motor, unless you can pull a motor over 300 rpm.
I don't respond to Private Messages PM's that are motor questions.
is this 50 psi an across the board thing for pull start motors? just asking, 50 psi seems soooo low for reliable running?!!! would really like to know (for future puchases of old motors) what is acceptable for comp #'s?. i've read many posts, and the lowest ive heard for a motor running ok is 60?? that even seems low for reliability. more concrete info needed here!
many men fish for years without ever knowing its not about catching one.
I don't know about concrete info, but if I were looking at an engine of that vintage and the compression was anywhere 50 psi or above and very close on both cylinders I would consider it good. If you were to run the engine and do a good decarb, you would probably see an increase the compression.
What are the factory cylinder compression specs for this motor, Model 3022? I can't seem to locate this info in my manual.
I have a comprehensive Johnson Service manual that gives all the specification from late 1940's to 1964. The guys are right, no compression figures were printed.
I have a 1957 Evinrude 3hp Lightwin and the compression numbers are 80psi on the top and 82psi on the bottom. Now that being said, it does not mean your motor is no good. A lot variables affect compression testing. It could your guage or your technique. *** The most important bit of information is that they are 10% of each other.
Your piston rings could be all coke up with harden carbon and preventing them from moving and effecting your compression. You can try facing your motor up (spark plug holes to the sky) and pouring a ounce of Seafoam in each cylinders and let it sit a couple of days. Replace the spark plugs back in the holes. Hopefully the seafoam with seep into the crevices of the piston rings and start to soften and dissolve the harden coke/carbon.
A very experience lightwin AOMCI forum member stated this about the JW and Lightwin 3hp motors.
80 to 90's psi, the motor idle very low and run like new
70 to 80 psi, the motor will idle low and run great
60 to 70 psi, the motor will idle decent and will run fine
Here is a link to the Iboats article on how to decarb your motor. Very good article.
Seafoam cost about $7 or $8.00, cheap way to decarb your motor and it will certainly not harm it.
Check your compressionnumbers after the decarbing and hopefully it will improve your numbers. Clean your plugs after you decarb the motor and torque them back to specifications.
Just a bit of friendly advice that was given to me. If the motor is running fine, don't get caughtup with numbers. If its a fishing motor and it gets you the fishing hole and back, then great. At 50psi, it you may have to idle it a little higher to keep it smooth, then again some people don't have boats or a motor to enjoy, so enjoy it!!!
Being cheap and not getting a manual will cost you hundreds or maybe thousands of dollars
I did a thorough re-read of the Evinrude factory service manual and no specs are given nor are any psi numbers mentioned. I will install the head and see what I get. Thanks to all that responded and provided helpful info.
I came into this life with nothing... and I have most of it left.