The Bolens lawn mower engine operates on the same basic principles as any gas-powered engine: Gas mixed with air ignites in a combustion chamber, forcing a cylinder head downward, moving the piston that turns the crankshaft, producing motive power. Troubleshooting the lawn mower most often requires determining which component -- gas, air or spark -- is missing. This will allow the operator to isolate the specific malfunction and make repairs. Troubleshoot your Bolens mower yourself; if you solve the problem, you've saved a few bucks.
Things You'll Need
Leather work gloves
Spark plug socket
Park the mower on a flat area of ground so you can work on it safely. Wear leather work gloves when troubleshooting. Lift the rubber boot, on the end of the HT lead wire, off the tip of the spark plug.
Loosen the spark plug with the socket wrench and remove it with your fingers. Secure the test plug into the boot on the end of the HT wire. Clip the test plug to a grounded metal point on the engine block.
Pull on the starter rope like you're trying to start it. Look for a blue spark to move across the points. If spark isn't present or it's a weak yellow, the problem lies in the ignition system. Check the entire ignition system for damage.
Disconnect the test plug and leave the plug wire and spark plug disconnected. Pull on the starter three times to purge the engine. Fit the compression gauge into the spark plug hole and tighten it with your fingers.
Pull repeatedly but not rapidly on the starter rope until the compression gauge meter stops increasing. Check the gauge for a reading of at least the minimum required for your engine (see engine specifications). If the reading doesn't stay constant or drops quickly, the lawn mower will need its compression serviced.
Unscrew the air filter box and remove it from the engine's side. Unscrew the choke or throttle plate from the top of the carburetor. Disconnect the fuel lines and watch if fuel comes out. If only a little fuel or no fuel comes out of the lines, the fuel system needs repair.
Lift the mower up slowly, with the carburetor side up. Wear work gloves and spin the blade with your hand. If blade doesn't spin adequately or requires extreme force, inspect the drive system for any damage.
Unscrew the recoil starter cover from the top of the engine. Lift the cover off and turn it over to check the recoil starter assembly. Hold the starter cover while pulling out on the starter rope. If it doesn't pull out or retract properly, inspect the entire recoil assembly for damage.
Leave all other troubleshooting to a professional to prevent engine damage and personal injury.