Compression on a 2000ish 150hpdi?

[Swift Buzzard]

2000-2001 Yamaha LZ150 hpdi
Not sure of the year due to the sticker having damage....
Computer says 197hrs (computer could have been replaced at some point) The motor is very clean, and even the skeg is barely missing paint.
P/O has only owned it for 2 seasons.....and has bought a bigger boat.

I just bought the boat and can only run it in the driveway. The motor starts right up and runs great on muffs. I am just going through everything so when spring comes I don't have too many surprises.

The only history I have on it, was that it was loosing rpm's and the previous owner paid $2700 This past summer for a new High pressure pump, and filters (Whole fuel system was done) Once fixed he said it ran great and used it all season. I have the paperwork from the dealer listing the work and YDS printout.

-Using a cheap tester-
Started motor and ran it on muffs for 5min (35f outside) Tested Dry

My bottom port cylinder #5 has 93psi and bottom starb #6 has 90.....The rest are 110-115. The motor runs great, just wondering if that is normal due to the different compression ratios? Bank to Bank they are very close. I also tried to do a leakdown test but my tester only goes to 20psi. At 20psi on the low cylinder I got aprox. 8% leak and 3% on the others.

Thanks...

[Swift Buzzard]

Please.....someone tell me to just do a de-carb and everything will be fine!

[robert graham]

With the variables in the compression tests maybe try running them again or have a Yamaha technician run them....bottom line, I doubt you have any compression problems.....

[boscoe99]

2000-2001 Yamaha LZ150 hpdi


-Using a cheap tester-
Started motor and ran it on muffs for 5min (35f outside) Tested Dry

My bottom port cylinder #5 has 93psi and bottom starb #6 has 90.....The rest are 110-115. The motor runs great, just wondering if that is normal due to the different compression ratios? Bank to Bank they are very close. I also tried to do a leakdown test but my tester only goes to 20psi. At 20psi on the low cylinder I got aprox. 8% leak and 3% on the others.

Thanks...

Was the motor fully warmed up? I would not think so if idled for five minutes at 35 degrees F. Was the throttle fully opened? Was the battery fully charged? Were all of the plugs removed? Was the motor cranked until the compression pressure stopped rising?

I don't think you have a problem if the motor starts, idles and runs well. The bottom cylinders on each side have a lower compression ratio. They would not be expected to have as much compression pressure as the two cylinders above them. If they did something would be wrong.

[Swift Buzzard]

I doubt the motor was warmed up...I could run my Merc EFI all day and it would not get up to temp!
The throttle was advanced and cranked for 10 sec...

I have read so much conflicting info for #'s on this engine...People saying they are getting 120+psi on all cyl's...If you do the math with the compression ratios this is a low compression motor and 110 would be high......
This is my first Yamaha so I have tons of learning to do! It idle's so smooth and quiet on Muffs I can't wait to take it for a blast!!!
Thanks....

[boscoe99]

I doubt the motor was warmed up...I could run my Merc EFI all day and it would not get up to temp!
The throttle was advanced and cranked for 10 sec...

I have read so much conflicting info for #'s on this engine...People saying they are getting 120+psi on all cyl's...If you do the math with the compression ratios this is a low compression motor and 110 would be high......
This is my first Yamaha so I have tons of learning to do! It idle's so smooth and quiet on Muffs I can't wait to take it for a blast!!!
Thanks....

There are usually too many variables involved to ever try and compare one model motor to another of even the same model. The pressure of the atmosphere changes daily, even hourly. Depending upon the ambient conditions the results will change depending upon when the test is performed.

Gauges rarely will indicate the same. People conduct their tests differently which provides different test results.

Compression pressure is just one of many measures that indicate the general health of a motor. It is not an absolute go/no go value.

[TownsendsFJR1300]

Please.....someone tell me to just do a de-carb and everything will be fine!

Yamaha has a product that works very well called RingFree :

https://www.shopyamaha.com/product/d...?b=Search&d=34.

Its works very well on both the fuel system and top end carbon. It does take a bit of running (don't expect overnight major differences).

You can also pull the plugs, tilt the engine up and add some Seafoam directly in the cylinders overnight to help loosen up crap.

** CRANK THE ENGINE OVER WITH NO SPARK PLUGS to push out excess SF so as NOT to cause a hydraulic lock when all done.***


I'd probably do one bank a time with the engine tilted up and to the side (so the piston(s) are as straight up as possible)..

[ausnoelm]

Toss the compression gauge back in the shed, go boating and enjoy yourself.