Grass is getting tall and you decide to mow your lawn. Your mower cranks and runs okay. You start mowing and 10 minutes later the engine stops and refuses to restart for 30 minutes. The questions come to mind of why did it stop, why will it not restart, what is wrong, and how to fix it.
Systematic Symptom Checking
Following the symptom checking systematically outlined here as a step by step will aid in reaching a correct diagnosis quickly allowing you to get mower back in operation and reduce your frustration.
How did the engine quit? Was it sudden, or did it sputter a few seconds before stopping. If it stopped suddenly it indicates the ignition failing. Possibly from a coil that is overheating and the 30 minute wait time allows it to cool and resume working. If you have a spark tester, use it to determine if the engine has spark.
If you don't have a spark tester, remove the spark plug and reattach the spark wire to the plug. Place the plug on an engine surface where its base will ground and crank over the engine while you observe the plug tip, looking for for spark.
Test for spark immediately after engine stops—if spark is not present when the engine is cranked, replacement of ignition coil is the repair in this case. Also check to see if one of your “rodent” friends has chewed the insulation off the kill wire that plugs on to the coil and caused it to short out.
It's also worth double checking to make sure you're not dealing with a simple blockage from too much grass.
If it sputtered a few seconds before stopping then it points to fuel starvation. This can be caused by a plugged vent hole in fuel cap as the gas being used from tank has to be replaced with air that comes in through the vent hole. Immediately after engine stops slowly open gas cap and listen for air being drawn into tank. If engine then restarts the problem is the vent in gas cap.
Either clean out the vent or replace cap with a new one. Check the fuel hose between tank and carburetor to see if it is collapsing or is plugged internally. Sometimes the float and/or needle in carburetor will stick and shut off gas flow. Disassembly of carburetor and replacing float and needle will be the cure.
The fuel shut off solenoid mounted at bottom of carburetor can also be a cause of engine shut down. This solenoid has a spring loaded pintle on it that shuts off fuel flow to carburetor main jet when engine is turned off. Intermittent electrical conductivity in the wiring harness that supplies this solenoid and/or failure of the solenoid itself can shut off an engine.
Disconnect this wiring harness plug and check for electrical voltage across the harness terminals with key on when the engine shuts down. Absence of electrical voltage here indicates wiring harness trouble.
Check wiring harness for pinched or abraded conditions or bad corrosion at terminals and/or plugs. If you find it has electrical power, plug it back into solenoid and listen for a clicking sound as you do so. This will indicate solenoid is operating.
On rare occasions, the rubber tip of the solenoid pintle becomes loose and keeps the fuel shut off even if the solenoid is functioning. For a full visual check of the fuel shut off solenoid, remove it from carburetor base and reconnect wiring harness. Cycle the key switch on and off and observe the movement of pintle. It should retract with key on and extend with key off. If solenoid does not respond, replace it.
If you have followed these steps, discovered the problem with your mower, and successfully repaired it, congratulate yourself for learning another set of DIY skills! Just think about the time and money saved from not taking your mower to the repair shop and the long wait, while the grass grows taller, before it could be repaired and you could return it to service.