Winter has finally passed, and you can now start thinking about getting the garden back into Spring and Summer condition. Being a responsible owner, you decide to check that the lawnmower is running well before you need to put them to use.
If a lawn mower doesn’t have a spark, it can only be one of four wrong things. The spark plug is damaged or faulty, the high-tension wire connecting the spark plug to the ignition system fault is broken, the start/stop switch is not working, or there is a problem with the ignition system.
You fill the lawn mower with fuel check that the blades are good enough to give a good cut for another season.
When you are ready, you set the choke, pull the cord, pull the cord, and pull the cord. After straining your patience and your back, you sit down to consider what could be wrong.
How To Fix A Lawn Mower No Spark?
Internal combustion engines need three things, delivered at the exact time to work. These are.
- Fuel
- Air
- Ignition
If any of these is not present or is delivered to the cylinder in the wrong sequence, the engine won’t start.
In a nutshell, these are the factors a mechanic would check to find out the cause of the problem.
For this article, we will assume that fuel and air issues have been ruled out, and a test has shown that the lawnmower has no spark.
To start the engine, you need the ignition system to send a sufficient electrical charge through the high-tension cable to the plug, which will, in turn, set off a spark.
As in all electrical circuits, there must be no breaks or unintentional changes in resistance to cause the ultimate spark.
The four elements which need to be investigated are.
- The Stop/start switch and the wiring connecting to the ignition system
- The ignition system
- The Spark Plug itself
- The Spark Plug Wire
If any of these items are broken, the circuit won’t close, and the plug will not create a spark.
How To Check The Stop/Start Switch And Its Components?
The stop/start assembly includes the following components.
- Bail Throttle Control Lever
- Cable
- Stop/Start switch
- Flywheel brake assembly
- Coil control wire
Bail Throttle Control lever
This lever can become disconnected from the throttle cable, either because the adjustment is out of whack or, more likely, the control lever itself is broken. To fix this, source a new one and replace it on the machine.
The Cable May Be Broken
If the throttle cable is broken or stretched, it will not close the circuit, and a spark will not be produced.
The Flywheel Brake Assembly May Be Faulty
If the flywheel assembly is faulty, it could very well just be an adjustment issue where the cable is out of spec.
If this happens, the bail lever won’t move the switch to the off position, and therefore no spark will be generated.
The Stop-Start Switch Itself
Most lawnmower engines have a start-stop switch that connects directly to the flywheel.
When the Bail control lever is activated, it pushes on the stop/start switch and closes the circuit to the coil; this allows the engine to start.
If the switch has broken, a spark will not be generated.
You can test the switch by carrying out the following steps.
- Attach the spark plug lead to the spark tester and connect the tester’s ground lead to the engine (to ground it).
- First, turn off the switch.
- Pull on the cord or turn the starter motor over and watch for a spark in the tester window.
- If you see a spark in the tester, the switch is not switching off.
- Move the switch to the ON position and repeat step 3.
- If you don’t see a spark, the switch is not closing the circuit and needs to be replaced.
How To Check The Ignition System?
The ignition system sequences the spark exactly when the gas and air mixture is in the combustion chamber.
If the spark is not generated or occurs at the wrong time in the combustion cycle, the engine won’t start.
Most modern lawnmowers have ditched the old contact breaker ignition system in favor of solid-state unis; It has no moving parts, and the machine’s reliability is increased. Solid-state units use a tiny transistor positioned in the coil or armature to close the electrical circuit that travels through the spark plug leading to the spark plug(s).
First Test The Coil
If your lawnmower is not producing a spark, you should test the coil; this is very quickly done as follows.
- Clip the spark tester to the ignition cable and the cylinder head.
- If it sparks, the coil is working, and you can move on.
Check The Solid-State Ignition Unit
With no moving parts, these units are very reliable. If it does fail, it is probably because of incorrect fitting, which has caused it to get too hot.
If you have tested everything else and this is the last potential culprit, we suggest that you take the lawnmower to a dealer who will have the necessary equipment to find out what is wrong.
How To Check The Flywheel Brake Assembly?
The main issue which affects lawnmower flywheels is a sheared flywheel key.
The flywheel key’s function allows the flywheel to move on the crankshaft when your mower blade hits a hard obstruction, such as a root or metal outpost.
If the mower blade is loose, it may generate enough shock energy to shear the flywheel key.
To check the flywheel key, follow the manufacturer’s instructions and replace it if necessary.
How To Check The Spark Plugs?
The spark plug must be in good order and set to the correct gap to generate the spark required by the engine.
In a real-life situation, we would not wait until this late stage to check the plug because they are easy to replace and reinstall.
- When checking the plug, make sure that there are no carbon build-ups between the ground and center electrodes.
- Check that the ceramic insulator is not cracked or chipped.
- Check that the gap between the ground and center electrodes is within the lawnmower manufacturers’ specs.
Spark plugs are not expensive, and if you have any doubt about the one fitted in the lawnmower’s engine, buy a new one with the exact specifications.
If this doesn’t fix the problem, it is elsewhere on the engine, but you have eliminated one factor.
Checking The Wires To The Coil
There usually are three wires which lead to the coil.
- The High-Tension Spark Plug Lead.
- The power wire connected to the ignition unit
- The ignition switch wire.
If any of these are broken, the ignition system will be disabled, and there will be no spark.
Conclusion
In this article, we have discussed all the possible reasons why a Lawn Mower has no spark. Likely the cause will be relatively simple, and when investigating, we recommend checking the most straightforward possibilities before investigating the more complex possibilities.
If in any doubt, ask a qualified lawnmower technician to diagnose the problem for you.
