Compression ?

I have a Johnson 150 VRO 1988 Model. The Oil injection was disabled by previous owner. Boat has been sitting for 2 years. I finally got around to mess with it fist thing I did was a compression test. All 6 cylinders are 75psi I think my gauge is ok but do not have another to test with. All cylinders are within 1/2psi from each other. I had a buddy say if the rings are dry it may need ran then recheck the compression. I started the motor for just a few seconds and it sounded great except I had to kill it the fuel pump was leaking so a new fuel pump is on the way but we did not run long egnough to test his theory. With the 75 psi should I be concerned since all 6 a all most dead nuts the same compression. Should I run it and recheck is it possible the compression can increase?

Re: Compression ?

Ideally you should check it after running it up to temp, but 75psi is in a normal range for a big, low compression V6.

Re: Compression ?

How can I verify if this motor is suppose to be low compression? I will run up to temp after i get new fuel pump in and retest though

Re: Compression ?

When an engine is cold evrything is as small as it gets so there is alot of leakage, warm you shoud gain quite a bit.

Having all cylinders so close is a good thing, I would say teating hot should get you up to 85-90 which is normal.

Re: Compression ?

90-95 is close to normal on this engine. Gauges do vary, so try to borrow another one-or rent one from your local NAPA dealer for the day. If the compression reads low on another gauge, you may want to run some Bombardier Engine Tuner through it and see if the compression comes up somewhat. I doubt you have a problem, since the compression is so even on all cyls. Compression can be affected by cranking rpm. If you have a weak battery, it will give lower readings. Make sure the battery is well charged. Some fuel/oil entering the carbs will provide adequate lubrication for taking a good reading.

Re: Compression ?

Just sold this boat got her running and compression was right at 90 when warm on all cylinders actually hated to part with it thanks for the help guys