Today I was riding and my bike fouled a plug. That was the first time I have noticed any problem with my Grizzly. It would idle fine at first, but miss and sputter under a load. Then I tried to climb a hill and it wouldn't make it. Finally it wouldn't even run. It appeared gas had been coming out of the over flow tube from the carb. Gas was no longer coming out the overflow. At that time I really didn't know what was wrong. I didn't know if I had a gas line off or leaking or what? I turned the petcock valve off and opened the gas cap. I seen a bunch of air bubbles rising in the fuel. I took the plug out and it was black everywhere. Put a new plug in. Air bubbles where still in the gas. Turned gas on, started it up, went up the hill. I stopped at the top of hill and looked in the gas tank, no air bubbles. Bike ran fine going up hill and still runs fine. Motor is stock, stock jetting, the only mod is a power tip on exhaust. If anything that should have leaned it out a little. Has anybody had this happen ?