951 DI Engine and Compression test (110 psi)

[mkeough11]

Do you have any idea what your impeller pitch is? Mine is 11/20.

 

[Bonmotwang]

My 2001 sportster le is 11/20 too. P/N 204 160 136


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[mkeough11]

Well we have the same impeller, same rpm & I would guess basically the same hull, yours a 2001 and mine a 2004, so I guess it comes down to weight? Do you carry more than 500 lbs? My wife and daughter and I weigh about 525 lbs. And I can easily go to 55 with no problems, so I am not sure why, with the same hull, impeller and rpm you do not get the same speed? Unless the hulls for the 2001 and 2004 are different.

 

[Sportster-2001-951C-Stock]

i think my impeller was replaced at some point b/c it has radiused(curved) leading edges and the others I've seen are straight. Seems to work fairly well as my WOT RPM doesn't bounce off the rev limiter. No idea what the numbers stamped on the impeller might be, haven't torn the pump down yet.

Our boats use the same impeller the LRV did, and I'm pretty sure it's a smaller wheel than the skis used.

Probably none of our speedos are correct, my pickup has four magnets on the rotating wheel, perhaps the later speedo system is a little different?

 

[mkeough11]

Mine also has 4 pickups. And the radiused curved impeller, I believe means it is a progressive pitch impeller. The straight ones are a fixed pitch. I know mine says it is a progressive pitch. I will know for sure about the speedo this Sat. I will use my gps and see how accurate it is.

 

[Sportster-2001-951C-Stock]

Mine also has 4 pickups. And the radiused curved impeller, I believe means it is a progressive pitch impeller. The straight ones are a fixed pitch. I know mine says it is a progressive pitch. I will know for sure about the speedo this Sat. I will use my gps and see how accurate it is.

That's interesting about the curved leading edges of your impeller, from the photos I've seen of Bonmotwang's I recall his were straight, unlike mine. Ya never know, someone may or may not have reworked mine but I'm pretty sure they did considering there was still a good size muscle shell caught in the intake grate I think the PO had a habit of operating in very shallow water.

Could be there are two different versions of the same impeller with the same PN I guess, ya just never know.

http://www.ebay.com/itm/Seadoo-Sola..._Watercraft_Parts&hash=item3ce4266044&vxp=mtr

 

[mkeough11]

Here is what is confusing to me. The link you posted was for a Solas SE-SC-XO 16/19 pitch, and it shows my part number. Yet my research shows that OEM part number to be a 11/20 pitch.

 

[Sportster-2001-951C-Stock]

I'm sure your research is correct concerning pitch. There were two impellers in that link and one of the Solas was incorrect for our boat but the other OEM impeller was the correct PN.

The seller just wasn't clear the two aren't the same impeller.

 

[Sportster-2001-951C-Stock]

Here's another thought, are you using the compression tester fitting that's the same length as the plug threads? If you use the short threaded fitting the reading will be lower due to the volume of the threaded hole that normally would be occupied by the longer fitting.

And, any leaks in your hose will cause the reading to skewed to the low side.

It's hard for me to imagine your engine is low on compression, considering how well it runs. Anyway, another potential sign of low compression might be above normal black carbon soot on your center plug electrode insulators along with more frequent fouling b/c as compression drops off the fuel mixture isn't as fully consumed during the combustion cycle.

 

[mkeough11]

Well I finally checked my speedo with gps and found that my speedo reads 5 mph faster than I am going. So when my speedo reads 55, I am really doing 50. Oh well, I will just keep that quiet when I have passengers in the boat. They always ask how fast are we going:thumbsup: Still runs great, just not as fast as I though!

 

[Sportster-2001-951C-Stock]

I guess one of these days I'll have to break down and GPS mine, measure compression again also, LOL, now I feel like I'm neglecting my Seadoo!

50MPH is pretty dang acceptable for this boat IMO, especially if it's able to accomplish that in a wide variety of conditions/wind/chop.

Yesterday I set the throttle at 5000 RPM and measured between 25~30mph on the speedo, noticed by rolling over from side to side slightly using the "tiller" could change the speedo reading briefly.

 

[beardo76]

Well those 951 compression on a perfect engine is 130 ( lower then a skidoo 2 stroke) so 110 is at the bottom of the acceptable scale.
Keep an eye on your plugs, its a good way to see how the engine is burning ( rich, lean)

My 951 was rebuilt in the winter, 5 mm base gasket ( vs the 6 that was previous on there) I get 120 cold compression on a 20 dollar compression tester.. Its running perfect at the moment.

As for speed, I get 55 mph on my phone gps when I am by myself ( 180 lbs) on water that has a 2 -3 inch ripple ( water calm as glass is actually a bit slower then water with a 2-3 inch ripple)

 

[Sportster-2001-951C-Stock]

55MPH is quite good Beardo, I'd say your boat's running great. I'm often too impatient to wait for those (calm) conditions and mostly mine only sees WOT during the hole shot.

 

[Sportster-2001-951C-Stock]

Umm, I learned recently the 951 DI blows a bit over 140~145psi in good condition more pressure than the carbed 951 motors do.

 

[Bonmotwang]

Umm, I learned recently the 951 DI blows a bit over 140~145psi in good condition more pressure than the carbed 951 motors do.

Are the two top ends same?


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[Waterluvr]

Are the two top ends same?


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The carb 951 uses a slightly larger bore 87.91mm versus the DI at 87.88mm, the DI runs another 20 PSI in compression over the stock carbed engine and uses a different cylinder and head.

 

[Bonmotwang]

The carb 951 uses a slightly larger bore 87.91mm versus the DI at 87.88mm, the DI runs another 20 PSI in compression over the stock carbed engine and uses a different cylinder and head.

I see, thanks for the info. By general speaking, is the DI an "improved" design over the carbed one?

 

[Bonmotwang]

I see, thanks for the info. By general speaking, is the DI an "improved" design over the carbed one?

Just watched Rotax E-TEC DI engine video, a nice design. But just worried about the oil delivery system is much more complicated than the carbed one. Or it is as reliable as the oil pump on the carbed ones?

 

[Waterluvr]

I see, thanks for the info. By general speaking, is the DI an "improved" design over the carbed one?

From a DIY point of view certainly not, it was simply one more step up in technology that existed solely to comply with government regulations such as the US EPA's CARB emissions compliance phase of the time. All of it was spoon fed to consumers as product and technology improvements by manufacturers of everything from boat motors to snow blower's but the bottom line is simply that very little of it would exist today had the EPA not declared a de facto war on 2 stroke engines by regulating exhaust emission standards at increasingly difficult phase levels of testing standards.

 

[Sportster-2001-951C-Stock]

My understanding is there are more than one cylinder port design for the 951DI as well, so make sure yours is correct for the MPEM fuel and spark map else it won't run correctly.