1998 1200 yamaha waverunner seal - Yamaha 12V Air Pump

Go to google to download

https://www.slideshare.net/GeraldGum/1989-yamaha-waverunner-owners-manual-95458948

Call Yamaha and tell them the serial number.

Yamaha did not make the GP model until 97 and if the numbers you posted are correct you have a 94, that being said all yamahas up until 93 were either a 500 or a 650 so im guessing its not a superjet which is a standup so you may have a waverunner 3, Raider, Blaster, or a wave runner LX. What colors are on it? does it have twin carbs? there will also be a sticker on the engine cases noting engine size.

check for corrosion of the engine as leaving it for long any water left in the system will cause problems.

https://www.jetdrift.com/yamaha-waverunner-3-650-review/

Gas oil mix 50-1

Have you done a compression test on all cylinders? My guess is you have a dead cylinder (no oil to one or more cylinders causing loss of power). If the compression test passes (all cylinders equal and higher than 100-110 psi) you have a restricted exhaust from a failed catalytic converter that has broken apart.

I have a 2001 waverunner and it stoped runing in the water . Now it will turn over but won't start

How do I reset the code on dash board 99 yamaha waverunner 800?

White smoke means coolant in the combustion chamber. Most likely a blown head gasket. You will have to tear the engine apart to be sure.