Yamaha Waverunner running bad?

[chi85]

I just de-winterized my jet ski and have had it out 3 times so far. 1st time it ran bad would only go to maybe 40mph and would bog down when I went full throttle. 2nd time it ran perfect, reached 60mph and ran great for 2 hours. 3rd time was nightmare, it would only do 20mph and would die or bog down when I gave fully throttle. I recently removed the carb and cleaned it but it wasnt even dirty, jets were fine. Could it be that I have bad gas from the jet ski being winterized for 7 months? Spark plugs are a little black but seem fine. Not sure what else to do. Any suggestions would be great before I end up taking it to the pros. It is a 2005 Yamaha GP800