Control Valve

Disconnect exhaust line to carburetor from the control valve. Seal off the end of the line. Increase engine speed to above 2000 RPM, but below 3500 RPM, and check if exhaust gas is blowing out of control valve. This may be done by placing finger by the valve to exhaust line connector. If no blowing of exhaust gas is detected, replace valve. Now allow engine to return to idle and recheck valve. If exhaust gas blows out of valve, replace valve.