96 Challenger - Low Top Speed

[TxState]

I've been working on a 1996 SeaDoo Challenger with a 787 Rotax and I can't get the top speed above about 33mph on smooth water. Top engine speed of 6,000RPMs*

Things I've done:
- replaced wear ring
- trimmed spark plugs wires
- cleaned rave valves
- rebuilt exhaust rave valve
- rebuilt carburetor

Losing my mind. Not sure where to go from here. Compression was roughly 130psi on both cylinders but I've read that a lot of guages aren't very accurate so the actual pressure might be different. The cylinders were giving identical readings though.

It's been getting a little bit better with each fix. Carb rebuild was the latest thing. It runs smoothly now but I just can't seem to get the top speed up. I've read that most people with this boat usually have RPMs higher than 6k at WOT. Any ideas would be appreciated.

 

[racerxxx]

You're shy on RPM should be around 6,900-7k


Borrow a gauge from an auto store, if you're truly at 130 it's time for a rebuild.

 

[TxState]

I did borrow a guage from an auto store. I've read that unless you have a high end compression guage, they're generally unreliable for an absolute value - that they're mostly only good for relative values.
Also, why would compression be low on both cylinders?

 

[racerxxx]

The harbor freight one i used and compared to my buddies Snap on read exactly the same number. Luck of the draw I guess, go to a different store and borrow another one. Just like a Dr. go for a second opinion.

 

[TxState]

Can I get away with just a top end rebuild to improve my compression?

 

[racerxxx]

Sure. But wouldn't you like to try another gauge for free or do you want to possibly spend unnecessary money?

 

[TxState]

I meant, "can I get away with just a top end rebuild to improve compression as opposed to an entire rebuild (top & bottom) of the engine?"

 

[racerxxx]

Yes, you can just do the top end.

 

[DerekI]

Also you have an accelerator pump on your carb. Could be the issue

 

[DerekI]

Also you have an accelerator pump on your carb. Could be the issue

Also you won't know until you take off the head if you need a full rebuild. FYI. 130 is low should be at least 150 but still 33 @ 6000 is low check the pump 1st.

 

[jts32]

No accelerator pump on my '96. Is the carb adjustment correct so both carbs open fully at WOT? Can you feel the raves opening when running? I think mine are adjusted to open around 4500-5k, and you can definitely feel the difference in power and rpm. New plugs?