I have stock 2000 Yamaha GP1200R - last year the jet sky was fast and trouble free. This year it runs at half speed. It limits RPMs to 3000 and when when you press thrutle it sound like RPM limitter is kicking in. The top speed now is only ~35MPH. It runs normal until it reaches 3000RPMs. Once on while the RPMs go higher when the jet sky hits a large wave, but can not maintain it. It goes down after few seconds.
I changed park plugs and they looked normal. Changed gas in the tank.
Any other ideas where I should look next?

Thanks,

Greg

Compression test will tell you lots.

How many hours up? Last re-build? Last carb. rebuild?

It has only 100 hours on it (total). I was never rebuilt. I will check compression tonight.
Thanks,

Greg

100 hours is the critical time on those engines.
Without doubt time for carbs and top end to be done, and it should be fitted with the powervalve clips that Riva sell?----most important.

(Not sure if I should mention the brand I used on mine all those years ago. Riva. Yes or no????)

It could be a simple as bad gas or a bad fuel selector switch. If you take care of this ski, 100 hours is nothing. If you have already did the mods such as cat con, wave-eater clips, and oil injection, something as simple as keeping fresh fuel and starting them every couple of weeks will give you trouble free riding for years.

I made a typo on RPMs. It cuts out at 5,000 not 3,000. The compression on 1st and 3 cylinder is 110 and the second is 112. The compression went up to 116 on 1st and 3rd and 118 on the 2nd cylinder with thrutle wide open.
Changed gas filter, but did not checked or changed fuel selector switch.

Thanks,
Greg

It might also be worth checking the PV's. Make sure the servo cycles as it should.

slowpole:
I have the same model and had the same problem. What I found on mine was the CatCon was blown out and was stuck in the pipe, not allowing full air to pass. This caused it to overheat pretty bad. I took exhaust apart and replace CatCon with D-Plate from Riva and put in a Oil Block Kit (pry not relevant here) and then i went from barely 40 MPH to 68MPH. Guess it's a lot of work, but take apart ur exhaust. You will probably find the cat con blown out (from my experience)

Bad cat-con or warped fuel flapper in the tank pickup.

Im with Full throttle on this one if it was a fast change in preformance. The cat con would be a slower loss of power. just my opinion. When you push the start button it should cycle the vavles. I am in the process of repairing the same thing. Going with gas valves and because the front valve started hitting the piston I am now going to do piston and rings and ,well while there, might as well do new reeds and maybe stuffers and what ever else.