2001 Yamaha 2 stroke 150hp compression readings

[cvillemudcat]

Hello, new to this forum and to Yamaha outboards.
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

[rodbolt17]

the 90* looper 225 jonny rude ran 80 psi.
what you are looking for is a bank to bank difference of less than 10 PSI.

[walleye1]

Every gauge reeds differet.

[BQUICK]

Make sure you have throttle wide open when checking. Also, motors sitting for a while and tested cold can show lower readings vs warm or recently run. Generally if they are all within 10% even 90 would be OK but I usually see 115-130 on those.

[99yam40]

2 strokes will scavage enough air from exhaust ports to do a compression test without opening the throttle.
try it open and closed next time you do a compression test to see what difference you get

[walleye1]

Does not matter as long each cyld is with in 10 percent of each other.

[cvillemudcat]

Thanks for all of the input. The motor was warm as we had just put it back on the trailer from running it. My mistake for not have the throttle wide or even partially open. I'm not sure how much that will effect the compression readings? All cylinders were 90 to 95 psi. I don't think much maintenance has been done on this motor other than changing the plugs. I also noticed it didn't have the OEM Yamaha tach. Does that OEM tach have an oil warning light or buzzer? I'm new to Yamaha and am not sure how the oil mixing pump warns the operator if something fails with the oil injection

[JerEazy2]

easy way to test the oil warning, turn the key to "on" and pull the oil reservoir cap off and see if the buzzer starts going off. There is a float in there that warns of low oil.

If you're a previous JohnnyRude owner like i am, i can tell you the Yamaha oil system is much better than the others out there. But, you absolutely need a service manual for your specific engine. They can be a bit quirky.

Also, there are multiple types of 2-stroke Yamahas - so whenever possible post up your model number

[rodbolt17]

OHHH ELL NO. DO NOT pull the cap.
to easy to simply pull the water trap, drain the engine tank.
turn the key and watch,listen.
you should get 3 bars flashing,an audible alarm and the transfer pump should refill the tank in 180 seconds.
yep it is that simple.
if you pull the cap any trash in the tank now heads for the pump intake and you have to retrieve and replace the seal,