We recently purchased a 1998 TRX 90, which I suspect had been setting for sometime.
It started and ran fine for a short time, then started sputtering and would hardly pull it self. I cleaned the tank, cleaned the carb by disassembling cleaning with starting fluid and blowing air through ports, the float valve seems to be working properly when I try to blow through it with the valve open/closed. It now starts easily, and runs ok at slow rpm, but when throttled up it starts to sputter. If I put it into neutral and let it idle for a few seconds, it seems to idle at elevated rpm, then returns to normal rpm. The engine does not show any signs of smoking when running.

Any ideas would be appreciated.

 

From my experience sounds like a carb issue .there are some very small orifices that you can't just blow out ,use a torch tip cleaner ,the smallest one usually and go thru everything again .This new fuel crystalizes badly ,also try using marine stabil (the green one) or an enzyme treatment w/gas ,helps in the future .Good Luck