Riding Mower and Tractor: Cranks but won't start
If the starter motor spins the engine but the engine won't start, the engine is missing one of its key ingredients for starting—fuel, compression or spark. Check your basics first. Make sure your fuel tank is full of fresh gasoline—the engine won’t start without clean, fresh gas. Check that your air filter is clean because the carburetor needs ample air to mix with the gas. Check the spark plug for fouling. If you have starting fluid and are confident that you can safely use it, spray a short burst of starter fluid into the inlet for the carburetor and try to start the engine. If the engine starts briefly using the starter fluid, then you know that spark and compression are okay so you can concentrate your troubleshooting on the fuel supply. You may need to rebuild or replace the carburetor to restore the fuel supply to the engine. If the engine doesn't start briefly using the starter fluid, then a compression or ignition failure could be the problem.
Here's a troubleshooting video that shows how to troubleshoot an engine that spins but won't start: Riding Lawn Mower Engine Spins But Won't Start Video.
These repairs may help solve your Riding Mower and Tractor problem:
Tune up the riding mower engine
The engine tune-up includes routine maintenance for a riding lawn mower or tractor. This tune-up includes replacing the engine oil, oil filter, air filter, fuel filter and spark plug. The tune-up also includes checking the ignition, carburetor, battery, throttle and choke controls, as well as cleaning the engine cooling fins.
Replace the air filter
The air filter traps debris from carburetor inlet air. A dirty air filter could be the problem if the engine stalls after starting or the engine runs rough or sputters. The carburetor won't get enough air to mix with the fuel for combustion if the air filter is dirty. Inspect the air filter regularly and replace it when dirty.
Replace the riding mower carburetor assembly
If the engine on your riding mower or lawn tractor is running roughly or only runs when the choke is partly on, you might need to replace the carburetor. The carburetor mixes gas with air before the fuel goes into the cylinder. If the gas/air mix isn't balanced, the engine won't have peak performance.
Rebuild the riding mower engine carburetor
The carburetor mixes fuel with air to create a combustible mixture that enters the engine cylinder and ignites to drive the piston. Impurities in gasoline can clog the carburetor. Seals and gaskets in the carburetor eventually wear out. Use a carburetor rebuild kit to refurbish a clogged or leaking carburetor.
Replace the riding mower fuel pump
The fuel pump moves fuel to the engine from the fuel tank on the riding mower or lawn tractor fuel tank. If the engine won't start or quits after starting, the fuel pump might not be working.
Replace the riding mower ignition coil
The ignition coil in a riding mower or lawn tractor produces the energy to cause the spark at the spark plug. The ignition coil is the likely the cause when the engine won't spark if, after you remove the kill wire, there's no spark from a known good spark plug.
Replace the riding mower engine fuel filter
The engine fuel filter screens impurities from the gasoline going to the carburetor. A clogged fuel filter won't allow gas to flow to the carburetor. A damaged filter won't screen impurities from the gasoline, resulting in a clogged carburetor. Replace the engine fuel filter if it's damaged or clogged.
Replace the riding mower spark plug
The spark plug gets electrical current from the ignition system and sparks to ignite the fuel mixture in the cylinder, which drives the piston. The spark plug won't spark if it's coated with carbon deposits or oil residue, or if there’s a crack in the ceramic insulator. The engine won't start if the spark plug is bad. Replace the spark plug if it's damaged or coated with residue.