POULAN PRO - 2014, 38" RIDING MOWER, PB145G38, ENGINE B&S MODEL NO 31R607-0005-G1 (585822301) 14.5HP, 499cc 1-cyl gasoline: Will not start at any position on the throttle. Will start if I cover the air intake with my fingers, runs with the air that slips past my fingers, if I spread my fingers...