http://www.triangleatv.com/Tips-Page.html this is from triangle atvs website, if youve plugged the carb drain tube, that might be it
Carburetor drain modification:
There is a drain/overflow tube, which runs from the bottom of the carburetor bowl down to an area near the recoil starter on the rear of the engine. This tube serves as both a carburetor bowl overflow and a drain. There is a small check valve near the end of the tube.
We have found that this check valve fails to prevent water from entering the carburetor bowl when riding deep water for extended periods. Therefore we plug the drain/overflow tube with a small stick or screw when riding deep water.
Be aware that plugging this tube prevents the carburetor overflow from functioning. This will cause problems in certain situations where carburetor overflow capability is required. Some of these situations include trailering (traveling) or riding in off-camber (tilted/side hill) situations.
Plugging this tube can cause the air box to fill with fuel when traveling and can actually fill the cylinder up with fuel to a point where the bike will not turn over (crank). We always remove the overflow plug and turn the fuel off when traveling.
Plugging this tube can also cause the bike to flood out in off-camber (tilted) situations such as when one side of the bike is in a rut and the other side is riding higher out of the ruts. This situation causes the float to allow fuel to run freely into the bowl faster than the engine can burn it. The bike will flood out and will not start until the overflow drain plug is removed and excess fuel is allowed to drain out. Fouling of the spark plug often results from this situation.