Need Help !!!

[1200man]

I have a stock 1999 Yamaha XL1200 Ltd waverunner. When I go to the lake the ski runs fine for about a half hour, then it begins to loose power as if it's starving for gas and cuts off. I've changed spark plugs, fuel filter, rebult all three carbs, changed cervo motor, replaced two powervalves, switched electrical boxes. I've also checked for water on my spark plugs. My compression is 118 on all three cylinders. I would appreciate any new ideas. Thanks, 1200man

[97GPSLEEPER]

This is just a wild guess, but maybe it has something to do with the catalytic converter. It maybe falling apart or getting plugged up.

[1200man]

Thanks for the quick response but I've already removed the cat and replaced it with a D-plate. If anymore ideas please reply. The engine is very strong turning 7000rpms for a half hour then just dies.
Thanks, 1200man

[jeffsntx]

Maybe you have an exhaust leak? Try running the ski with the seat off and see if it still happens. If the ski has an exhaust leak, it will fill the engine compartment and "snuff" the engine.

[1200man]

Thanks, I'll check that because the motor is performing but after 30 mins still dying out. appreciate your help!
Thanks, 1200man

[LT1GMC]

Two thoughts come to mind:
One, is the venting and associated check valves working and installed correctly, because that could cause a decrease of fuel flow over a period of time as vacumm builds in the fuel tank.
Two, I've had more than one time the handlebar start/stop switches go bad, and just shut it off like it ran out of gas, sometimes restarting right away, sometimes after sitting a while. Acted just about like you mentioned. I know it sounds weird, but its happened on three different units I've had over the years.

[Duke]

I would bypass the fuel selector valve and give it a try.

[philip_gpr]

I would bypass the fuel selector valve and give it a try.

Good idea, just hardwire the carbs direct to the reserve line.

[RX951]

check the gas tank vent and see if the hose is not kinked.
also slightly loosen the gas cap and see if it goes away.

[1200man]

Hey fellows, thanks for the new ideas. Tomorrow, I'll take it to the lake and try them. I was also told that the stator and pickup coil could be causing me these problems. These were the only electrical components that I did not change. What do you think???
Thanks, 1200man