How to Troubleshoot Mower Carb Problems

Examine the choke or primer for proper function if cold starts require repeated attempts. Remove the air filter housing and place a teaspoon of gasoline into the carb. Start the engine. Restored performance indicates problems with the choke or primer. Some chokes are manually engaged by a cable or knob, while automatic chokes employ a thermostatic spring for actuation. Make all checks and adjustments recommended by your mower's manufacturer. Replace any primer assembly that exhibits leaks or requires repeated manipulation.

Clean the internal passages of the carburetor by adding fuel system cleaner to the mower gas tank, because engine stalling that occurs after start-up may signify restrictions in the carb. Disassemble the carb, and clean the parts and passages with aerosol carb and choke cleaner if problems persist. Adjust the governor spring if stalling occurs when a load is encountered, such as when mowing tall grass. Closely follow the manufacturer's specifications for your mower's governor spring adjustment.

Adjust the carb mixture screw clockwise to lean the mixture and eliminate gray smoke emanating from the exhaust of a warmed engine. On most mowers, gray smoke indicates a rich air-fuel mixture. Adjust the mixture screw counterclockwise to increase fuel flow and correct popping or sputtering exhaust notes. Consult the repair manual for your model mower if the screw is sealed, or you don't see any improvement. Add fuel system cleaner to the gas tank if no adjustment is allowed or suggested.