You already know whats wrong, the needle valve doesnt cutoff the fuel. several reasons: 1. the float chamber has a hole 2. the valve, valve seat or float is bad or misadjusted. 3. there is dirt between the valve and seat. Did you try the advice from the other posts? A good carb rebuild kit will give you a valve, float, valve seat if yours is removable, gaskets and instructions on how to set the float .some times you get drawings or pictures. Did you check Freds in MA resources or google "carb rebuild"? Good luck.