Compression for 1986 pro v 150 j

I have lost all top end on my pro v 150. Was running fine, then all the sudded just came off plane. I cannot get it to get on plane. I ran a compression test w/ all plugs out w/ the following results: 44,45,50,45,45,50. Everything I've read on here says they should be w/in 10 % of each other, so that part looks ok, but I also see that most engines are around 120-125 psi. I removed the head and the gaskets showed no sign of blow-by. The cylinder walls look smooth...no scarring or pitting. Anybody know why readings would be so low? Is this a low compression engine? ( engine code isro v 150J 6J9 L 302425) Thanks, Mark.

[boats.net]

That is low, check your compression gauge to see if accurate.

Borrowed a Snap on guage set from local auto mechanic to do that test. He said it works fine. I cannot redo test at operating temp obviously w/ the head off now. Would it make that much difference? I sprayed some oil in the cylinders and it brought it up 5 - 10 psi. Still seems mighty low. Did Yamaha make a low compression version ? Thanks for the input, Mark.

[jb123]

most likely you were looking at the wrong increments, maybe kg's?

it should be from 100-125. more than likely you have a carb issue.

Carbs were rebuilt 2 yrs. ago. I disconnected fuel hose after fuel filter and used priming bulb to check for gas flow. I pumped it into a clear container and the first 5- 6 gallons was cloudy and orange colored. Let it stand for a couple minutes and it separated. Caramel orange color on the bottom ( about 20 ounces ) and a cloudy yellow on top. Kept pumping until I got clear gas. That must have been the problem. As for the compression, my auto mechanic came by and did the test w/ the same results. He was wondering if having all the plugs out was the proper way to test a two stroke boat engine. Could we have been losing compression through another cylinder? I think the gas was my problem but the low compression still has us baffled. Thanks so much for any input on this, Mark.

Was just reading a post by MAVERICK7. He described ethanol separation occuring in his fuel tanks. His description of the fuel he drained is exactly what mine looked like. Just went to boats.net home page and read about ethanol fuels and what they do to marine engines. This was new to me. Many of you probably already know about this but if you don't, go to the home page and read the " attention boaters" link !!!

Did a shock treatment w/ Quickleen and it helped, but still ran rough. Pulled the carbs yesterday. It looked like they were full of sand! Upon close inspection of the debris in the bowls, it looked like small orangy crystals. I think this is the separated ethanol that has crystalized. Has anyone ever seen this stuff before? I cleaned the carbs and now it runs like a new boat. I'm running Quickleen in the fuel because the only outboard dealer w/in an hours drive is a Merc dealer. I'll borrow my mechanics compression guage Monday and recheck and post results. Hopefully the compression reads higher.

[jb123]

carbs still dont explain low comp readings you got....

Yea I know, but I'm thinking that maybe the rings were carboned up , and a good run on the water w/ Quickleen might free them up and bring up the compression.

[Hamfisted]

Using a Racor filter ?

Mark do you have a Racor fuel/water separator installed between the fuel tank and the engine? I didn't see that mentioned is the only reason I ask. Those old carbs are a pain in the butt to keep clean. The idle jets are located at the bottom sides of the bowls and they clog up real easy. Have to run the motor at least every couple of weeks to keep them clear. Run Sta-Bil in the fuel too.



- Mike

Hamfisted, I did just install a Yamaha 10 micron water/fuel sep. filter. Was just relying on the little filter on the motor. Just ran it again today after adjusting carbs.When the boat shop rebuilt carbs 3 years ago, they adjusted carbs and it took 5-6 seconds to get on plane. I don't have a manual , but I adjusted them after cleaning them they way I used to adjust my old Holly carbs on my street rods. It jumps up on plane now in 2-3 seconds! Thanks for the tip about Sta-bil. My local Merc dealer sold me their fuel stabilizer. Do you think it is adequate or do you recommend Sta-bil brand?

Checked compression today. 47 psi in all cylinders. Boat jumps on plane in 2-3 seconds and runs strong. Turns 5000 rpm's at about 50- 55 mph. Gonna try a different guage tomorrow. Shouldn't run this good with these compression numbers. Guage has to be wrong.