99 Yamaha Waverunner wont go over 3o mph!!!

[newtoboating76]

I have a 1999 Yamaha GP800 waverunner, I had it out last year, ran fine, would run about 55 mph with no issues, I didn't drain gas, I only disconnected the battery and covered it up, this year, I replaced the battery, the plugs and gave her a drink of seafoam and she will not run over 30 mph, I can give it gas and it takes off with power, then it stay at 30 mph, I can hold the throttle down and it seems there is about 4/5 seconds of holding it, then the waverunner seems to want to take off and goes to like 34 mph then stops and returns back to 30...anyone have any advice...I am new to the waverunner scene

 

[Ronnie]

This forum’s focus is more on jet boats not pwcs but someone here may chime in. In anycase, i suggest you also seek answers from dedicated pwc forums like greenhulk.com .

my two cents on your issue: you have a two stoke motor so it’s supposedly simpler to work on. Since the ski starts and keeps running it’s not an electrical issue. It’s not likely to be a fuel issue either. If you have bad fuel or no fuel is getting to the engine the ski would not limit itself to 30 mph. So I assume you have have an air issue and recommend that you check that the air intake and filter are clear. It wouldn’t hurt to do a compression check as well a check that each spark plug is firing. If you are running on less than all of your cylinders you would probably notice that the skis is running rough or that the motor doesn’t idle well or that it cuts out unexpectedly.

goof luck.

 

[Cobra Jet Steering LLC]

It is usually BAD GAS that causes those symptoms ,especially when you are taking it out after storing it over the winter. Another would be exhaust leak inside the hull cutting down the oxygen levels look for bad exhaust hoses or missing clamps.

 

[biffdotorg]

The last time I had this issue happen on a GP machine it was a GP1200r. The 800 is the two cylinder version of that animal.

Tow major things if it's not as simple as bad gas.
1. Reed valves should be checked. If one is chipped or broken it will not pull full throttle as fuel is not passing properly or at the wrong time. They will chip and break. Not overly expensive to replace, but you need to know where to find them in the throttle body. A set of reed for your 800 is around $65

2. Catalytic converter in the exhaust manifold. That honeycomb piece can start to disintigrate and mine literally turned sideways in the cavity. To replace it is stupid expensive, as Yamaha thinks they are made of Gold/Titanium. If yours has failed, the most common fix is to remove it and install a D-Plate to maintain the back pressure that the cat provided. There is also a chip that overrides the O2 sensor that is disconnected.

Some of this may not apply to your vintage GP800, but it may as well. I am not seeing the cat and O2 sensor on the 99.

Good luck,