Wouldn't crank, took carburetor apart and cleaned, put back on, cranked first pull, cut grass, stopped and started, cranked right up. 3 days later wouldn't crank again sounded just like before. Bought new carburetor, installed, cranked first pull, stopped it cranked right up again, cut grass. Week later will not crank again, sounds just like it did initailly. What would cause it to crank right after I clean and replace the carb but not few days later.