The Great 951 Rpm Caper (Missing Rpm)

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CreekerMike

CreekerMike

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Greetings and salutations to all. Im back for more of your input and answers!
Since my last thread I have finished the assembly of my 98 Gtx Ltd with the new headgasket and have water tested it. No Leaks! But im still missing some Rpm.
Im hitting 6500-6600 while before I was hitting 6950-7000k every day all day.
I have not toyed with anything since changing the head gasket except for my water regulator. That i adjusted between 2.5 and 3.5 turns out with no large change in rpm...
So my question to you all, Where should I start looking for these rpm? New plugs, clean raves, Toy with water regulator? What else? My flame arrestors are clean, I rebuilt my carbs about 25 Hours ago (With an OSD kit) im at a loss here.
Something changed between blowing the headgasket and now. Any input is greatly spreciated!
 
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The first thing to check is compression. Did you have baseline compression numbers from before the head was pulled?
 
JeremyD615 said:
The first thing to check is compression. Did you have baseline compression numbers from before the head was pulled?
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Both mag and pto cylinders read 135 psi when I originally built the engine with a fresh sleeve and piston. I can check this number tommorow.
 
That’s a good number for a 951. Hopefully you’re close to that now... Outside of lower compression, I’d suspect that something is going on with that water regulator... I’ve used clear vinyl tubing from the regulator to the pipe to check for flow, but that’s a temporary thing for diagnostics. The vinyl tubing won’t last long in that application, so be sure to change it back once you’ve got it sorted...
 
Also you should never turn the adjuster on the water regulator. THey are set from the factory and I have never seen anything on where or how to set them. I can check my 2001 XP if that helps.
 
mikidymac said:
Also you should never turn the adjuster on the water regulator. THey are set from the factory and I have never seen anything on where or how to set them. I can check my 2001 XP if that helps.
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Miki I recall seeing a thread with a page from a service manual saying to bottom out the adjuster then come out 3 turns. I gotta ask though, if its not meant to be adjusted then why would they give it the cap with the adjuster.
 
CreekerMike said:
Miki I recall seeing a thread with a page from a service manual saying to bottom out the adjuster then come out 3 turns. I gotta ask though, if its not meant to be adjusted then why would they give it the cap with the adjuster.
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I assume they had some way of testing them at the factory so they could "dial them in" so to speak.
I know some of them they even used washers from the factory to "shim" the spring to adjust the pressure even though there is the adjuster.

I'll check my XP for you and count the turns in.
 
mikidymac said:
I assume they had some way of testing them at the factory so they could "dial them in" so to speak.
I know some of them they even used washers from the factory to "shim" the spring to adjust the pressure even though there is the adjuster.

I'll check my XP for you and count the turns in.
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Thanks miki, i just snagged a compression tester. Ill be home shortly and ill test the compression. Hopefully that blown head gasket didnt cook the rings or slightly bend the rod.
 
I know the spec on the 787’s is three full turns out, but I haven’t seen anything on the 951 skis...
 
Compression was a little lower than ide like but it was even between both cylinders to my suprise.
 

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That is still pretty low. At 110 the engine is done and looks like you are about 114, perfect is 130.
Time for a rebuild in my opinion.
 
Just to make sure, you did not use the same compression tester than the first test? I have seen variations of up to 15 PSI between two different testers.
 
I would take another tester first. Just an example: bought a tester at $50.00 a few years back and tested my own ski that had been rebuilt 30 hours before. It showed 135 while it was supposed to be more near 145. Had a friend who tested with a professional tester and it gave close to 150. I thought I had lost around 15 PSI in 30 hours too but my tester was a bit off. I don't trust my tester anymore or at least I know it is about 10-15 PSI off.
 
benjilafouine said:
I would take another tester first. Just an example: bought a tester at $50.00 a few years back and tested my own ski that had been rebuilt 30 hours before. It showed 135 while it was supposed to be more near 145. Had a friend who tested with a professional tester and it gave close to 150. I thought I had lost around 15 PSI in 30 hours too but my tester was a bit off. I don't trust my tester anymore or at least I know it is about 10-15 PSI off.
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I should be able to get another compression tester off my buddy at work tommorow, ill report my findings then.
 
Little update-I swapped plugs and went out on the river. The motor definately sounds healthier and its gained about 100rpm.
It seems like itl hit 6950 for a few seconds at WOT and then fall off back to 6800 then 6700..... i could this be a fuel issue or is there something else at play?
 
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CreekerMike said:
Little update-I swapped plugs and went out on the river. The motor definately sounds healthier and its gained about 100rpm.
It seems like itl hit 6950 for a few seconds at WOT and then fall off back to 6800 then 6700..... i could this be a fuel issue or is there something else at play?
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Generic seadoo TROUBLESHOOTING guide...fwiw
 

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I don't chase engine RPM but it is a measurement that can be of value. What was your top speed? That is a measurement that is the sum total of all things and is also my fun meter measurement. :D If you're having fun on the ski.... ride it like you stole it. Don't worry about compression numbers till you have a performance problem that doesn't change or gets worse. Compression doesn't heal itself, it deteriorates or can stay at a low number for a long time without ill effects.
 
I’d take a close look at that water regulator. They cut the flow of water down at high rpm, so if it’s not sealing well, it can rob you of som revs...
 
JeremyD615 said:
I’d take a close look at that water regulator. They cut the flow of water down at high rpm, so if it’s not sealing well, it can rob you of som revs...
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Where in the water regulator should I start? Is there a good thread or write up on how to inspect/ repair one? I have pulled it apart before and i saw nothing of concern. The boot was good, the clamps were all intact, and the shaft was screwed in snug.
 
etemplet said:
I don't chase engine RPM but it is a measurement that can be of value. What was your top speed? That is a measurement that is the sum total of all things and is also my fun meter measurement. :D If you're having fun on the ski.... ride it like you stole it. Don't worry about compression numbers till you have a performance problem that doesn't change or gets worse. Compression doesn't heal itself, it deteriorates or can stay at a low number for a long time without ill effects.
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In my book this is a performance problem. Before i had a rpm i could sit at all day long. One head gasket later and bam im not hitting that number anymore. Though this may not be a cataclysmic issue, it could be the start of one. In my head this issue needs to be resolved.
 
I dunno about those water regulators.... they are a mystery to me. As you did, I took mine apart and played with everything... tried to understand how it works. I didn't see a problem and when I put it back on the ski, o gains were noticed. Then... before leaving for a ride, I swapped Water Pressure Regulators from a different ski. The ski was much better in the top range of RPM and it was noticeable. I never figured that one out. LOL
 
Pull the head then and have a look if it all started with a head gasket replacement. You have a compression number that doesn't seem correct for the amount of hours. I'd start there.
 
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