Either the needle or the float. the float can be set too low and it doesnt seal off the gas inlet. place your carb upside down and with the gasket in place and measuring calipers measure from the gasket on the carb body to the top of the float. Bend the tabs on the float either way so that each little float measures at 21mm. Also the most common way to tell a needle is bad is by looking closely in the light, you may see a ring goings around the tip. That is a major indication that it is bad.