Sure sounds like a dirty carb, but I´ve had a cracked reed do exactly that some thing. They´re easy to change. I use the Boyeson Rad Reed and got the RB design carb mod, which well worth the money. Reeds are about 35-40 bucks and RB design carb mod was $160.00 or so. I´d start with the reeds if you´re sure that the carb is clean. If that gas is more than 2-3 weeks old, I would definately change that. It´s amazing how bad the gas effects 2 strokes.