Dirt from the air or fuel is hands-down a carb's biggest enemy. Dirt will build up and clog idle jets and orifices, making your carb run like crap. Misfires and stuttering are common symptoms. Make sure to thoroughly clean out any dirt you find in the float bowls. The better your air filtering agent, the less dirt you'll suck into your carburetor. For the absolute least amount of dirt in your carb, we'd probably recommend using a cheapy paper air filter, and replacing it every 5,000 miles, along with a high-quality fuel filter.