you probably have some crap in the bottom of the gas tank that is getting picked up. Run an in line fuel filter (in addition to the stock one) and that should keep things clean. Fuel stabizer is good if you plan on having the motor sit for extended periods of time with out use. Gas will turn into a varnish like solution when it sits for too long and gum everyhing up. Unfortunately draining the carb completely out of gas doesn't always get it all out. Gas can get stuck in small ports and metering rods.