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I have a 77 115hp johnson engine which i just did a compression test and they all came out in the 60 range. I bought a new compression tester from harbor freight and my battery was ok. Could it mean it needs new pistons or what? Thanks.
100 psi is considered minimum ideal number.You could try a "decarb"treatment with something like sea foam, just follow the directions.
Wouldn't hurt to try a different tester.
Does it seem under powered?
Also there can be a 50 psi difference between warm and cold engine. Run it until it is up to full temp then check it before it cools down. And what Steelespike said too.
Racerone has the correct compression info. I'd expect a factory fresh 115 to have around 125 lbs on each hole. Testing compression without the spark plugs removed will result in low crank rotation speed, which will absolutely affect compression numbers. Doing a decarb on the engine can bring the compression readings up somewhat, but not usually 60 lbs. Worth a try, tho.
If all cylinders are 60 not just one or two of them I'd say your gauge is off. Did you use one you screw in or hold in the hole ? And as noted above all plugs should be removed,carb butterflies open all the way,think this was also noted above a motor at operating temperature will produce higher readings than a cold one.
