You turn the ignition key and can hear the engine wanting to start, but it just won’t.
A Cub Cadet zero-turn cranks but won’t start when it isn’t getting air, spark, or fuel.
This may be due to a plugged air filter, incorrect choke setting, bad spark plug, plugged fuel filter, clogged fuel line, bad fuel pump, dirty carburetor, or old gas.
Take caution when working on your mower. This includes always removing the spark plug wires before performing repairs.
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Follow all safety instructions provided in your equipment operator’s manual before diagnosing, repairing, or operating. Consult a professional if you don’t have the skills, or knowledge or are not in the condition to perform the repair safely.
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This is Why Your Cub Cadet Zero Turn Cranks But Won’t Start
1. Stuck Choke or Wrong Choke Setting
The choke is used to restrict airflow so the Cub Cadet engine runs rich allowing more fuel and less air into the combustion chamber. This is required to start a cold engine.
When the engine warms up, the choke lever must be adjusted to the off position so the engine gets enough air to continue to run.
SOLUTION: Like a cold engine won’t start without the choke engaged, a warm engine won’t start with the choke engaged. Having the choke set correctly is required to start your zero-turn.
If the choke is set correctly and you are still having airflow issues, check to make sure the choke plate is not stuck. Use carburetor cleaner to help free up a stuck choke plate.
Also, check that the choke cable is moving freely. Use a lubricant like Sea Foam Deep Creep or a similar product to free up the linkages. Replace a damaged or worn choke cable.
2. Plugged Air Filter
Another airflow restriction you may have that may cause your Cub Cadet to crank and not start is a clogged air filter.
The air filter is a required part used to keep dirt out of the air intake. Dirt getting into the air intake and to the engine can cause permanent engine damage.
While the air filter is used to protect the engine, it can cause damage to the engine when it isn’t kept in good condition.
A lack of airflow due to a plugged air filter may not only keep the engine from getting sufficient air to start, but it may also cause the engine to overheat.
I recommend starting each mowing season out with a new air filter and then cleaning it several times throughout the season. Of course, if you are using the mower more than the average homeowner, you will need to clean and replace the filter more frequently.
SOLUTION: Follow the instructions below to clean a zero-turn air filter. If you are unsure what type of filter you have and its cleaning instructions, find the information in the lawn mower operator’s manual.
Clean a zero-turn lawn mower PAPER air filter:
Take caution when working near the engine as the engine can be hot.
- Remove the air filter from the housing.
- Wipe out any dirt remaining in the housing. Be careful to not let any dirt fall into the air intake.
- Tap your filter against a solid surface. What you are trying to do is knock as much dirt out of the filter that will come loose and fall out.
- Hold your air filter up to a light source and make sure you can still see light shine through the paper element. If you can, go ahead and reuse your air filter. If you can’t or the filter is damaged or very dirty, it’s time to buy a new one.
- Reinstall the air filter and attach your air filter housing cover.
3. Dirty Spark Plug
Remove the spark plug using a 3/4″ or 5/8″ socket wrench. The size you need depends on the engine model used on your lawn mower. Inspect the condition of the plug.
A spark plug that is damaged or very dirty can cause an intermittent or lack of spark required for the engine to start and run. When looking at the spark plug, check for a burnt electrode, broken porcelain, or dark-colored tip.
SOLUTION: If you find any of these conditions, install a new spark plug. If the plug is in good condition and just a little dirty, clean it with a wire brush.
Reinstall the spark plug after you ensure the gap is correct. Then securely attach the spark plug wire.
Because a good spark plug is essential to a good performing lawn mower, I recommend starting each season out with a new spark plug.
4. Old Fuel
Gas doesn’t stay fresh for very long. It actually can begin to break down as quickly as 30 days after purchase. Old gas leaves behind varnish and sticky deposits that cause fuel restrictions and component failures.
Because of this, it’s important to purchase fresh gas and consume it within 30 days. Stay away from gas with high ethanol levels. Only use gasoline with a minimum 87 octane rating and a maximum 10% ethanol content.
Read more about the right gas for a Cub Cadet zero-turn here. I share more information about choosing the right gas, the negative effects of ethanol, and how to care for the fuel.
SOLUTION: If you find your zero-turn has old gas in the fuel tank, drain the fuel tank using a fuel siphon pump. Fill the tank with fresh fuel with a fuel stabilizer mixed in.
I like the product Sea Foam Motor Treatment to help clean the fuel system and reduce moisture. You can read more about fuel additives here.
Allow the lawn mower to run so the gas and fuel additive works its way through the system. If you aren’t able to get it started yet, continue reading to troubleshoot other fuel-related items that can cause your starting problem.
5. Plugged Fuel Filter
A fuel filter is used to keep dirt out of the fuel system. Your zero-turn will use an inline fuel filter placed between the fuel lines. It strains fuel as it comes out of the fuel tank to keep dirt out of the carburetor and engine.
The fuel filter can become plugged when it isn’t replaced regularly. This will prevent a good flow of fuel from being able to pass through the filter and may cause the mower to turn over and not start.
SOLUTION: Replace an old or dirty fuel filter with a new fuel filter.
6. Clogged Fuel Line
Next, follow the fuel line coming out of the fuel tank to the carburetor. Look for any kinks that may be restricting fuel flow causing the lawn mower to turn over but not start.
If you don’t find any kinks, check for a fuel restriction in the fuel line. Do this by first shutting off the fuel flow using the fuel shut-off valve or fuel pinch-off pliers.
Check each section of the line by removing the end of the line furthest from the fuel tank and placing it in a container to check for sufficient flow after turning the fuel supply on.
SOLUTION: When you aren’t getting sufficient fuel flowing through a fuel line, shut off the fuel supply and remove the fuel line from the mower.
Spray carburetor cleaner into the line. This is used to attempt to loosen the clog. Then, blow compressed air through the line to dislodge and remove the clog. Repeat using the carburetor cleaner and compressed air until the clog is removed.
Reinstall the fuel line once the clog is removed. Replace it with a new fuel line if the restriction is not removed or you find the fuel line is aged and beginning to crack.
7. Bad Fuel Pump
A mower uses a fuel pump when the carburetor is positioned higher than the fuel tank. The pump is required to work against gravity to move fuel uphill to the carburetor.
Most zero-turns use a vacuum fuel pump. This style of pump uses the vacuum off the crankcase to get fuel to the carburetor.
When the fuel pump cracks or fails to work correctly you will have to replace it. If you don’t see physical cracks or fuel leaking, you can take some steps to check the condition of the fuel pump.
Before you test the pump, make sure you are getting fuel to the inlet port on the pump. (If you are not, check for a blockage in the fuel line or fuel filter)
Once you have confirmed fuel flow to the pump, remove the fuel line from the carburetor and place it in a container. Check your pump is working correctly by starting your fuel flow and starting your mower.
SOLUTION: You should have a steady or pulsating flow of fuel coming out of the fuel line. If you do not, you need to replace the fuel pump.
For other types of fuel pumps like an electronic fuel injection pump, refer to your operator’s manual for fuel pressure specifications. Replace the fuel pump if the pressures are lower than the specification required by the engine manufacturer.
8. Dirty Carburetor
The carburetor’s function is to mix gas with air to form combustion in the engine. When the carburetor fails to work, your lawn mower will not start.
Too often, the main culprit of a carburetor not functioning properly is old gas. Old gas leaves behind a varnish that may plug the fuel jet or cause the internal components to stick.
SOLUTION: When you find the carburetor isn’t working, you’ll need to attempt to clean it, replace any faulty parts, or replace it with a new one.
Before you tear apart your lawn mower carburetor, do this first:
- Confirm you are getting good fuel flow to the carburetor.
- Remove the air filter.
- Spray carburetor cleaner into the air intake and start the mower. If it turns over and starts using the carburetor cleaner, but then begins to run sluggish and possibly shut off once the carburetor cleaner is burned, chances are your carburetor is dirty. *Don’t use starter fluid*
- Proceed with disassembling the carburetor and cleaning it or replace it with a new one. You can find cleaning instructions here.
9. Plugged Fuel Tank Vent / Bad Fuel Cap
The fuel tank must vent to equalize the air pressure inside that tank to the atmospheric air pressure. On a lawn mower, the vent is located in the gas cap.
When the vent becomes plugged and no longer allows air to pass through the cap, the fuel tank forms a vacuum. This vacuum keeps gas from getting to the carburetor. The lawn mower will turn over, but not start because of the lack of gas.
SOLUTION: To determine whether or not your gas cap is the problem, loosen the cap and attempt to start the mower. If it starts, the gas cap may be the cause.
To further confirm the cap as being the problem, continue to let the mower run while tightening the cap. If it begins to sputter, shuts down, and won’t start again until you loosen the cap, you must replace the cap with a new one.