85-90 PSI Compression Test But We Did It All Wrong


Participating Member
I paid to have a compression test done on the boat I just bought. The results were 85, 90, 90, 90, 95, 95. Guy said that was fine. But now I'm reading up on it and wondering about that. Looks like those readings should be 100 psi or better. You can't believe everything you read on the interwebs but it reads like the engine should have been warm, throttle should have been wide open, and we should have used a fully charged battery. We had none of that. Batteries were dead and we had one of those jumper packs (it was enough to get it started easily when we got to that), the throttle was closed, and we did it cold.

2000 2 stroke 200XL EFI. We did it wrong... if we had done it correctly would it have improved or worsened the numbers?

The engine has been sitting for at least a year. When we ran it with muffs it produced a lot of smoke, but the age of the gas is unknown, at least a year old, and no idea on how it affects oil to sit there in that tank. It cycled up and down with the RPMs... ran it for maybe 5 minutes. Still a lot of smoke.

Any comments on this OB that I just bought? Yikes?!

Yep, and doing it correctly will yield better results. Not sure I'd go back to that mechanic. He should know better.
Yep, and doing it correctly will yield better results. Not sure I'd go back to that mechanic. He should know better.
OK, so at least the numbers would have been better rather than worse. That's a relief. Yes... I will go to the shop I have regularly used for the OB on my sailboat. Thank you Harper.
Would have liked to seen better (higher numbers) but near as important, the spread looks good and you usually do not want more than a 10% difference across the board...

A leak down test is a better measurement for overall engine sealing / health, though those steps for that 2-smoke engine need reviewing before proceeding with that test since some reed type of valves, usually do not seal up as well as the poppet types found in 4-strokes.

Run some quality pure synthetic 2 stroke oil in it (Like AMSOIL) and some Startron in the fuel to help break free some of that crud, and she will clear up (some) they don't call them "Mosquitos Killers" for no reason and that engine is basically just a Fuel Injected Chain Saw ;)
2-smoke. Funny! Haven't heard that before. Fuel Injected Chain Saw... even funnier! A good laugh. Yes, the variance looks good, and we did the test wrong ($75 and they did it wrong, sigh) so I'll hold hope that the OB has years left in it. I'm taking it over to a shop I have years of experience with to have it serviced for the season... impeller, lower unit, tune up. Will see what I learn there.
Get a portable 6 gallon fuel tank and try running it off that. Will eliminate the fuel as a variable in how it runs. Running the carbs thru an ultrasonic cleaner and reassembling will take care of any deposits left in the carbs by old fuel. You may be able to burn the gas in something like an old pickup truck.