Looking for some input on compression readings as this is my first time dealing with a Yamaha outboard. I'm looking at a bay boat with a 2001 Yamaha 150hp 2 stroke. My compression results were all in the 90psi range for all 6 cylinders. The lake test was good except for a mid range stumble that would go away if you push in the key to squirt a little more fuel in. So it has a fuel issue that needs attention; but what about those compression numbers? I have always had Rude and Johnson motors and good working compression was in the 105 to 120 range. Does anyone know the normal compression range on a carburated Yamaha 2 stroke 150 hp made in the early 2000s? Any input would be appreciated as I'm looking to decide in the next day or 2. Thanks

Had that fuel issue before and it was water in mine.

Thanks and yeah that may be the case on this one too. I just really want to be sure about those compression numbers before I buy this thing. Normal compression readings, anyone?

Hot or cold compression check? Was throttle full open?

Hot, it was right after the lake test. I didn't have the throttle plates wide open, but that never made much difference when doing compression checks on Johnny and Rudes. Not sure if Yamaha would be much different in regards to that. No hour meter, so hours are unknown.

It will result in lower compression readings on Yamaha's. From everything I've found on 2000 to 2003 150 HPDI's you should be seeing around 110 psi on hot motor with throttle full open.

Ok, thanks for the input. Do you think with the throttle plates closed it could result in a 10 to 20 psi lower reading?

Sorry, no idea what the reduction amount would be.

You need to recheck it with the throttle fully open, it will make a difference. As for 90, that is borderline low enough to not even ignite the fuel.

Thats low & getting near rebuild time

My 1999 vmax 150 read 125 on 1 cylinder and 130 on the others. I suppose some gauges could read differently though.