1997 Seadoo XP, carbs or something else

[Talbachi]

So I decided to check the piston squish to the head.., based on what could get at I'm measuring about .078-.093 for my squish with the gasket on, which seems way to much. It is entirely possible that I wasn't fully against cylinder wall and would then have a reading of .0625 to .078. I need to really buy some calipers... I will be checking it metal to metal to verify. If indeed it is that reading what are my options? I assume i would need a thinner base gasket? where do you recommend finding a .4mm gasket? I'm assuming I have .5mm gasket in there from SBT.

 

[JJinSC]

One more thing on the carb settings from the manual. 1.0 on the LS is not correct either. The setting should be 1.5. That runs well here at sea level. I’m not sure what that will mean at elevation. But 1.5 is the setting for this engine in that year ski.

 

[Talbachi]

So...the story continues. I tore into the top end today and cleaned everything up. the pistons, rings, and cylinders all look good. There was a little bit of sand in the front cavity where water flows just below the base gasket, and I believe that my base gasket has been leaking to the outside of the engine. So I am definitely going to be replacing that. Appears to have the .5mm base gasket from SBT in there. hard to tell, was not in great shape. I think its around 18 or so years old.

It would also appear that my engine is over sized? the top of the piston says 1.00. What does that mean. 1.00mm over sized cylinders? i thought that it only had a .25mm over size allowable.

 

[Ckrawiec]

According to the shop manual...the XP stock cylinder size of 82 mm, First overbore = 82.25mm.
The cylinder gasket thickness is "adjustable" for the combustion chamber volume.....there are holes in the gasket to indicate the thickness - 3 holes = .3 mm, 4 holes = .4 mm, etc up to 8 holes (7 holes is skipped). Did you/were you able to notice/determine the gasket thickness used / what was already there?

 

[Talbachi]

The existing gasket was a 5 hole gasket.

 

[Ckrawiec]

Reminder that this is an XP, not an SP. The existing gasket was a 5 hole gasket.

Yes, I editted my post as soon as I realized I was mistaken....

 

[Talbachi]

As a follow up trying to understand the oversize, means more combustion area, so it would theoretically need more air, which would need after market FA's? Wouldn't I need less squish to get to the same "stock" combustion chamber volume?

 

[mikidymac]

No, even with a 1.00 mm overbore you don't need to change any carb settings.

 

[Talbachi]

Hey, its me again. This summer was crazy. My 7 year old got a kidney transplant at the end of June, so we weren't able to get the ski out again until the end of August and now its cold here and I wont have the ski out again until next June. Utah is a crappy place for watersports...haha.

So after my rebuild of top end and am getting 130 psi compression, which I am ok with. Tried both high octane and low octane fuels and didn't notice a difference. I feel like my carbs are pretty good. on my last day out this year I was able to get 52.8 MPH measured by GPS. Maybe I could get more if ski didn't have a bunch of gelcoat wear from beaching by previous owner.

So my problem that I do have, Sometimes it feels like the ski grabs the water really well and just rockets, other times it feels like water blowing through the pump. I had replaced the impeller and the wear ring and oil all earlier this year. No rocks have hit impeller, and gap/lack of gap on wear ring looks ok.

If I am doing a pivot turn at about 25MPH and dig nose in, the engine will rev when impeller is out of water(as expected) and then just sits and revs once back in water and has little propulsion unless I lay off the throttle and let revs settle and then it seems to grab and go.

What do you think the issue is?

 

[Mraw]

When you changed the wear ring did you use a neoprene seal or any black rtv to seal the pump to the hull?

 

[Talbachi]

When you changed the wear ring did you use a neoprene seal or any black rtv to seal the pump to the hull?

no... should I have? there was nothing there before.

 

[Lothsahn]

Yes, otherwise air can get sucked in the joint between the hull and the pump and cause cavitation.

A neoprene seal is the recommended method, although others have used silicone or rubber gaskets. Silicone makes a mess, bonds with the fiberglass, and can be difficult/impossible to cleanup when you pull the pump again. Buy a $6 neoprene seal and do it the right way. Replace the neoprene seal every time you pull the pump.

Since you said you have a good impeller and a good gap (or lack thereof) on the wear ring, you have two remaining possible causes of cavitation:
1) No seal between pump and hull OR
2) Worn carbon ring

If I were you, when I pull the pump to put the seal in, I'd check and/or replace the carbon ring too. If your carbon ring gets *really* worn, it can even "sink" (really, more like swamp) your seadoo, but cavitation is the first symptom.