Why Would My Lawn Mower Backfire & the Exhaust Pipe Get Red Hot?

Inspection

• Caked on dirt can act as an insulating jacket and disrupt heat dissipation. The engine should be freed of any such build-up. Repair or replace any damaged or missing engine shrouds that may be necessary to direct airflow over the engine. The fins on the flywheel dispel heat through radiation and act as fan blades to generate airflow. Proper airflow is vital to engine cooling, so replace any flywheel that has missing or damaged fins.

Maintenance Issues

• Any leaking gaskets revealed after cleaning the engine can contribute to overheating. Replace any leaking gaskets and repair any other leaks detected. Check and adjust the oil level according to manufacturer's recommendations. Oil reduces friction and low oil levels allow excess heat to build rapidly. A clogged air filter can restrict engine intake and crankcase venting. Restore intake airflow and crankcase venting by replacing any air filter that exhibits build-up in the pleated paper element.

Spark

• An incorrect spark plug gap can alter spark timing and cause overheating. Clean or replace a plug that exhibits deposits on, or any defects of, the center and side electrodes. Deposits can foul a spark plug by preventing proper spark, and any cracks in the insulating ceramic will result in misfires and backfires. The plug center electrode should be flat at the end, and any loss of material here signifies the need for a new spark plug.

Fuel

• Fuel that has been in storage for a month or more can lack volatility and should be discarded and replaced with fresh fuel. Check the gas tank cap and ensure the vent holes are clear and unobstructed. Venting is necessary for proper fuel delivery. A lean mixture is caused by insufficient fuel and it overheats engine parts. To richen the mixture, adjust the carburetor mixture screw according to manufacturer's recommendations. Seek professional assistance if symptoms persist.