Try tapping in gently first, if this does not help, you will probably need to clean the carb. Carburetors are delicate, so either have your carb cleaned professionally, or follow the instructions with a carb cleaner.
You can try a can of BK44. If that doesn't work you may have to take the carb off and clean it. You can use a carb clean can from a auto parts store. It looks like a paint can and it allows to soak the part parts and loosen any build up.
