Low compression on all cylinders

[Mrfixit290]

I have a 1975 Mercury 1150 115 hp, the previous owner claims in was running 1.5 years ago when he parked the boat. I just did a compression test and all of the cylinders were between 72 and 85 psi. Should I try something like ring free or what should be the next step? I am wondering if I should get another engine or continue trying to fix this one? Thanks in advance!

 

[Mrfixit290]

BTW all spark plugs were removed, engine cold.

 

[The Force power]

I would RE-check the compression-readings with a different gauge. (your readings are too low)
Run the engine & check

 

[MPrimeaux]

I have the papers where the previous owners of both of my older mercs had the compression checked at a shop and tested waiver 100psi. Both of them run. I got less than 65 psi on all cylinders of my 650 and about 75 psi on all cylinders on my 500. I’ve also tested a 6hp evinrude at 45 psi on both cylinders and a 5 hp honda four stroke at 85 psi. All with the same el-cheapo amazon special compression gauge. I’ve tested the actual gauge with my air compressor regulator and the gauge reads accurately. I suspect there is something going on with the hoses or seals to my tester, but for whatever reason it doesn’t read accurately. My point is, ALL of the engines I mentioned run well and NONE of them are hard to start. May want to verify those readings with another gauge before you do anything to your engine.

 

[MPrimeaux]

Also...did you open the throttle all the way while testing?

 

[MPrimeaux]

I would RE-check the compression-readings with a different gauge. (your readings are too low)
Run the engine & check

I’m sorry man.... I keep doing this!! I swear I’m not meaning to repeat you. I’ll pay more attention!

 

[Mrfixit290]

Also...did you open the throttle all the way while testing?

This is a 2 stroke engine, I thought you did not have to open trottle.

 

[Mrfixit290]

I would RE-check the compression-readings with a different gauge. (your readings are too low)
Run the engine & check

I am using a cheap harbor freight compression tester, I will recheck with a different one.

 

[racerone]

Absolutely no need to open the throttle on a 2 stroke to get a good compression test.

 

[Mrfixit290]

Absolutely no need to open the throttle on a 2 stroke to get a good compression test.

Thanks