At what RPM does it do it? It's probably running lean which is pretty bad for the engine. Try to clean the carb and check whether there's something clogging your fuel lines. You can also try raising your needle (move the little washer down a few notches). If what I said doesn't fix it, you should go up on the jetting. You won't get it first try, so it's best to buy a jetting kit for your carb, but if you're cheap like me you could buy a few jets about 2-3 units apart (for example, if you have 110, go for 112, 115, 118...). If you want to ride and don't want to wait to get jets, you can try to restrict the airflow to the engine by plugging the air filter frame, though I don't recommend it.
