Thread: Scary low compression

If it's a 2 stroke I'm thinking rings
4 stroke valves
Did you have all spark plugs out during tests?
Was the battery fully Charged?
We're the intake ports open and Clear?
Doesn't sound good

4 stroke
Plugs out
Forgot to open throttle plates
Battery good
Intake not sure

Will redo today with warmed up motor, WOT?


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you been using non ethanol fuel? Treating your fuel?

for anyone that runs a yamaha 4 stroke engine, or any engine for that matter, i HIGHLY recommend buying a bottle of "yamaha ringfree" fuel additive. its pricey, but that bottle will last you a very long time. It will save your engine longterm.

Be sure the choke is open and throttle plates are open.
It may be a build up of carbon on the valve or valve seats.
I'm not sure if I'd recommend it but I've seen mechanics put a small amount of automatic trans fluid in the cylinder to free up stuck rings if that's the problem.
If the compression doesn't come up once it's warmed up it may be time for a professional opinion.
It may be cheaper to replace rather than repair.

Originally Posted by pete

you been using non ethanol fuel? Treating your fuel?

for anyone that runs a yamaha 4 stroke engine, or any engine for that matter, i HIGHLY recommend buying a bottle of "yamaha ringfree" fuel additive. its pricey, but that bottle will last you a very long time. It will save your engine longterm.

Thanks Pete
I put in sea foam
Will add ring free too



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Seafoam is great for a quick clean, but its actually recommended you not use seafoam for the newer 4 stroke engines.

Kind of strange that all cylinders are low. Usually just one or two go bad. Any chance the tester is faulty???

Originally Posted by SeaRay

Kind of strange that all cylinders are low. Usually just one or two go bad. Any chance the tester is faulty???

Yeah, I would try another gauge even if the one you are using is new.