You may have too much fuel pressure. Put a gauge on the fuel line & check it. It should not be over 4-5 lbs. If it is dirt getting in the needle & seat, try this trick. Put a vise grip or clamp on the rubber fuel hose to block it off. Start the engine & run it till it dies or starts to die. Take the clamp off & start it again. The rush of gas will usually flush the particle through. If the first time doesn't work try again. If that doesn't work then go to plan B. It's a good idea to put an inline filter in the line between the tank & pump. Also there should be a filter in the inlet of the carb.
