Riding Lawn Mower Won't Start
- Gas Valve Off
- No Gas
- Choke Fault
- Plug Wet / Faulty
- Plug Wire Off
- Bad Battery
- Air filter Blocked
- Gummed / Faulty Carburetor
- Coil Failure
- Faulty Control Module
- Flywheel Timing Off (Shear-key)
- Engine Compression / Valve Fault
Check The Basics
Mower Cranks, But Won't Start
What is Gas/Air Mix?
The Problem With Ethanol
What Is Spark?
What Is Compression?
The Gas Shot Test
Begin with clean fresh fuel.
The Choke System Test
Test Choke Operation
Otherwise, go ahead and remove it.
This will give you a better view of the carburetor.
Apply full choke.
Not necessary to remove this intake pipe.
You can see into the choke plate to check its operation.
Here I have removed the pipe so you can clearly see the choke in the full on position.
This is the correct position for starting a cold engine.
If the choke plate is not moving to the closed position, adjust cable so that it does.
If you found no issues with your choke system, check out "Carburetor Cleaning".
The Spark System Test
Note: The best way to test spark is with a spark tester tool, as it will load up and stress test the coil.
Remove the spark plug and check condition. Refit the plug wire and ground the plug on the engine, really well.
Have a helper turn the key while you check for spark.
Now try a new spark plug.
At this point you have:
Good spark - Move on and check Compression.
No or weak spark - Move on to next step.
Look for obvious signs of damage. Arcing and corrosion of the plug cap, check it fits snugly and securely.
Chafing of wiring against the engine is common.
Remove the engine cover, if not already removed.
Locate coil control wire connector.
Remove the coil control wire, you may need a Pliers.
Now check for spark as you did earlier.
Do you have spark now?
No, still no spark - Replace coil it's faulty.
Yes, have spark now - Check the coil control wire from the coil to control module (or ignition switch) for chafing and shorting.
If you found no fault with the wiring (try wiggling) - Then go ahead and replace the control module.
If your mower doesn't have a control module fitted - then replace ignition switch.
Fitting A Coil
The Shear Key
Remove cover, if not already removed.
Remove both bolts, and put one side.
Remove plug wire and push on wire connector.
If you can, get OEM parts, they are tested.
Nobody likes revisiting the same job.
An air gap must be maintained between the coil and flywheel. A business card is just the right thickness.
Tighten the bolts while keeping a push on the coil towards the flywheel. Remove business card by turning the flywheel.
Nice work, now rebuild in reverse order.