Look at your throttle shaft. Its 70 years old, worn to hell and causing avacuum leak! This is the 97/81 style, but it works with 48 and 40 modelsif you use the 9526-97 accelerator pump rod. The bushings compress oninstallation so ream them through (0.278″) to insure the correct clearance.Note: This item is ineligible for return or exchange.