ScootsUSA 151-185 - 7258 QMB139 Carburetor Idle Jet - 40 Carburetor Idle Jet for 50cc 4-stroke QMB139 engines. Choose from #30, #32, #33, #35, #38 and #40 jet sizes. Overall Length: 28mm Thread Size: M6x0.75 Available in Sizes 30, 32, 33, 35, 38 and 40