Maxim with 60psi in all 4 cylinders

My 1980 Yamaha maxim which I bought to revive is only running 60psi in All of the cylinders, at first they were running 30psi absolutely bone dry then I put a cap of oil in and it was running at 45psi in all 4 cylinders from there I waited overnight and it started running at 60psi… all 4 of them are consistent with how much they increased which confuses me because they have individual carbs valves and cylinders so they shouldn’t be so consistent theoretically it may be important to note it’s been sitting for about 20 years does anyone know what could be up? Tomorrow I’m gonna start to take apart the engine so any hints on what to look for would be great thanks

 

is this the first bike you have used that compression tester in?
I ask this cause I got a Compression test kit from HF and the #'s were half what they were supposed to be.. I knew that was wrong cause I the bike seemed to run pretty good. I then got another one from a different vendor and the numbers were more than double what the HF gauge was.
I took it back.

 

It's possible the piston rings are corroded/sticky. A mixture of ATF and acetone is alleged to do wonders. I used a couple doses of PB Blaster followed by ATF over a couple days and it doubled compression from 60 to 120. After a few hours run time it's up to ~135. Gonna run a couple bottles of Yamaha Ring Free through it this spring to see if it improves any more. I'd give that a go before tearing down the engine.

 

Stuck piston rings. Engine strip not recommended at this stage. Try the acetone ATF mix a few times and adjust valve clearance and redo compression tests. Also check twice with another compression tester. Pressures being equal across the cylinders is a good sign. I am not surprised they are low considering how long is has been sitting.

 

I assume you held the throttle wide open when you cranked the engine with a fully charged battery when you did the compression test??

 

Yes I did it was completely open and was maintaining 60 funny enough the first time I did it I didn’t have the throttle open and it was also 60

 

Need a little background on the bike pls. How long has it been sitting? The previous owner (PO) had it stored inside, outside?

If the bike has been sitting in a non climate controlled area for yrs with no one doing any maint on it, I would also go with the stuck rings. The chance that all four of them at bad or that low do to bad rings would be just back luck. As stated above, mix that solution up and let it sit in there for a good few days to a week. Then crank the motor over with a rag on each open spark plug hole to clean out the solution.

Once that is done give it a good check and maybe this time if you can get another tester from a friend or a auto parts store on lone. That way you can test the test, so to speak, to make sure you are getting good readings.

Is the bike currently running?

 

Do not tear down. Get it running.

 

Did you check the valve clearances?