got a '96 magnum 425 that is fouling plugs in hours, It did have 3 year old gas that smelled like lacquer thinner so i drained that and put fresh in it. But its just dont seem to have an top end power, only goes about 35 mph and it sounds like its getting carburator issues but i don't know what. The last plug looked to rich. Could the carburator need cleaning or is it out of adjustment. No ones messed with it so i don't know why it would need adjusted, altitude is 900ft.

 

Probably got a plugged main jet in carb from the thinner. From about 1/4 throttle to full throttle the Main Jet, Main Air Passage, Needle Jet and throttle valve supplies fuel at mid to high throttle. I'm reading this from a polaris manual! Must be clogged from old gas...remove ..clean and try again..You didnt say if oil or gas fouling

 

Take the carb off and clean it out real good and change spark plug this should take care of your problem.

 

ok I'll try cleaing the carb and let you guys know