You just want to cut the grass, but your riding lawn mower isn’t cooperating. It turns over but won’t start. The good news is that there’s only three possibilities to diagnose the problem.
The bad news is diagnosing the problem.
Tools Needed (Commissions Earned)
Any small engine requires three things in order to run: air/fuel mix, compression and spark. As long as you have those three things, the engine will run.
If your riding mower will turn over, that’s a good thing! It means that the engine is not seized and the battery is adequately charged for turning the engine over.
However, if it’s not starting, that means it is lacking one of the aforementioned three things.
Check for Spark
The first thing to do is to check for spark. Remove the spark plug and set the spark end on the metal of the engine body. This will allow it to ground. Turn the ignition and look for spark to jump from the plug to the metal body.
If you see spark, then you know that there is one required component. If you don’t, then assess further.
Check the condition of the plug, the wiring, and diagnose the coil. Clean the plug and confirm the gap is correct.
Check for Compression
While the plug is out, throw a compression tester in the plug hole to confirm adequate compression.
With the correct adapter installed into the plug hole, turn the key over and gather a reading on the pressure gauge. It should be in the vicinity of 90ish PSI.
If it is dramatically low, that’s an indication of inadequate compression. The causes for this can vary between worn rings, a stuck valve, a dropped seat, a blown head gasket, or other internal damage.
Oftentimes, we see low compression from a machine that’s been sitting for years or simply abused.
If it is your normally maintained riding mower, it’s unlikely to be a lack of compression unless there’s been some catastrophic damage.
Check Air/Fuel Mix
The fuel system of a riding lawn mower can be somewhat complex. Oftentimes, it involves the fuel tank, air filter, fuel filter, fuel pump, and carburetor.
You need to assess and diagnose each component to ensure that the engine is receiving the correct air/fuel mix.
This can be as simple as a plugged jet in the carburetor or as complex as a faulty fuel pump. With regular maintenance and a systematic winterizing procedure, most fuel issues can be negated.
Recap
Regardless, if your riding lawn mower is turning over but won’t start, rest assured that the problem is related to one of three things: spark, compression, or air/fuel mix.
Simply go through the procedures to diagnose and repair what’s needed in order to return your machine to working condition.
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