Lawn Mower: Can't Turn Engine Off

If your lawnmower won’t shut off, it could have a faulty ignition switch. The ignition switch actually works in the opposite way that you might think it would. When the engine is running, the switch is in the off position. When you want to stop the engine, the switch is turned on, creating a path to ground. The electricity previously flowing to the spark plug now instead flows to engine ground, and the engine stops running. The ignition switch is easy to diagnose. Setup a multi-meter to test for continuity. Attach the meter leads to the terminals on the ignition switch. With the control bail left in the off position, the multimeter should show continuity, there should be a circuit through the switch. Pull the control bail to the run position and the multi-meter should show no continuity. If the switch fails the continuity test, it will need to be replaced. Replacing the ignition switch is an easy repair. Depending on the engine design you might need to remove the engine cover to gain access to the ignition switch. First, note the location of each wire attached to the switch and then remove them. Now you can remove the switch from the engine. The switch is typically secured to the engine with a couple of screws. Install the new switch. You might need to adjust the switch or the switch actuator so the actuator makes good contact with the switch. Once the new switch is installed, reattach the wires.

The control cable is attached to the control bail on the mower’s handle and controls the ignition switch on the engine. When the control bail is engaged the control cable pulls the ignition switch actuator back, allowing the ignition switch to open. When the bail is released, the cable allows the actuator to spring back, closing the ignition switch and shutting off the engine. The control cable is attached to the lawnmower’s handle with clips or cable ties. The cable is exposed and can potentially be damaged. It can snag on a low-hanging tree or a shrub. This can bend the cable or the cable’s housing. If the mower is stored outside in the elements the cable is exposed to rain and dust. The water and dirt can cause the cable to rust and bind up with corrosion. Any of this damage to the cable can cause it to no longer operate smoothly. The cable may bind up when the control bail is engaged, causing the cable to not retract when the bail is released, holding the ignition switch in the run position. Replacing the control cable is a pretty easy repair. Start by removing any clips that secure the cable to the handle. In some cases, you will need to cut the cable ties securing the cable. Next, undo the connection between the cable and the control bail. Now you can disconnect the cable from the bracket and ignition switch lever, usually located near the engine’s carburetor. Install the new cable in the reverse order. Attach it to the bracket and lever on the engine. Reconnect it to the control bail. Finish by re-securing the cable to the mower’s handle. Be sure to replace any cable ties you might have cut while removing the old cable.