I replaced the oil, air filter which was very dirty, and cleaned the carb. and the mower just does not seem to have max rpm's that is did when it was new. when I sprayed the carb with the carb cleaner and stuck the straw that comes with the can in the carb the rpm's actually raised to the max and was running fine, but when i removed the straw it lowed back down. what do i need to do to get it running at it's max? thanks