9 Causes of a Cub Cadet Zero Turning Crank But Not Starting

When you turn the key, you hear the engine trying to turn over, but it won’t.

A Cub Cadet zero-turn mower will turn over but refuse to start if it isn’t receiving air, spark, or fuel.

Possible causes include a filthy carburetor, old gas, a blocked air filter, a clogged fuel filter, a clogged fuel line, a faulty fuel pump, a clogged fuel line, or a clogged spark plug.

Be careful when you fix your lawn mower. Always disconnect the spark plug wires before working on an engine.

Possible Causes of a Cranked But Unstarted Cub Cadet Zero Turn:

  1. Faulty or jammed choke mechanism
  2. Air filter obstruction
  3. Soiled spark plug
  4. Wasted gasoline
  5. Stuck fuel filter
  6. Fuel line clog
  7. False fuel pump
  8. Unclean carburetor
  9. Bad gas cap or blocked fuel tank vent

Before diagnosing, repairing, or operating, be sure you’ve read and understood all of the safety recommendations in the equipment’s operator’s manual. If you don’t feel confident in your ability to conduct the repair safely on your own, it’s best to call in an expert.

Your Cub Cadet Zero Turn Cranks But Doesn’t Start For These Reasons

1. Choke Got Stuck or It Was Set Wrong

To make the Cub Cadet engine run rich, with more gasoline and less air, the choke is utilized to restrict airflow. This is essential for cranking a cold engine.

The choke lever needs to be moved to the off position so the engine can receive enough air to keep running after it has warmed up.

SOLUTION: Just as a cold engine will not start without the choke engaged, a warm engine will not start with the choke engaged. To get your zero-turn going, you need to make sure the choke is set properly.

If the airflow is still erratic after adjusting the choke, the problem may lie with a stuck choke plate. If the choke plate is stuck, you can use carburetor cleaning to assist remove it.

Also, make sure the choke cable has free motion. To loosen the connections, you can use a lubricant such as Sea Foam Deep Creep. If the choke cable is frayed or worn, replace it.

2. Filter Blocked with Dust

A clogged air filter is another possible cause of your Cub Cadet’s inability to start after you’ve turned the key.

To prevent debris from entering the engine, an air filter must be installed. Damage to the engine can be caused by dust entering the air intake.

The air filter is supposed to keep the engine safe, but if it’s not maintained properly, it might really do more harm than good.

If the air filter is blocked, the engine won’t get enough air, which could prevent it from starting and lead to overheating.

A fresh air filter should be used at the beginning of each mowing season, and it should be cleaned multiple times throughout the season. If you use the mower more frequently than the typical homeowner, the filter may need to be cleaned or replaced more often.

SOLUTION: For cleaning a zero-turn air filter, follow the procedures below. The operator’s manual for your lawnmower will tell you what kind of filter you have and how to clean it.

How to change the paper air filter on a zero-turn mower:

Be careful when working close to the engine, as it can get rather hot.

  • Take the filter out of its housing.
  • Remove any lingering dirt from the case by wiping it down. Don’t let any grime get into the machine’s air filter.
  • Strike the filter against something substantial. The goal is to loosen and dislodge as much dirt from the filter as possible.
  • Check that light can still pass through the paper element of your air filter by holding it up to a light. Reusing an air filter is recommended if at all possible. If you can’t clean the filter or if it’s too dirty or damaged, you should get a new one.
  • Cover the air filter housing and replace the filter.

3. Spark Plug Gunk

Use a socket wrench measuring either 3/4″ or 5/8″ to take out the spark plug. Depending on the make and model of your lawnmower’s motor, a specific size will be required. Check the plug for damage.

If your spark plug is dirty or broken, you may not get the spark you need to start the engine. Look for a darkened tip, charred electrode, or cracked porcelain on the spark plug.

SOLUTION: If you see any of these symptoms, replace the spark plug. The plug can be cleaned with a wire brush if it is in otherwise good shape but unclean.

After checking the gap and reinstalling the spark plug. The spark plug wire must then be attached tightly.

A new spark plug at the beginning of each season is highly recommended because of how important it is to the mower’s performance.

4. Used Fuel

Gasoline doesn’t have a long shelf life. It might start to deteriorate as soon as 30 days after purchasing. Fuel constraints and component failures are both exacerbated by the varnish and sticky deposits left behind by old gas.

For this reason, fuel should be purchased regularly and used up within 30 days. Avoid using ethanol-rich gasoline. Use only gas that has an octane value of 87 or above and contains no more than 10% ethanol.

Here you may learn more about what fuel works best in your Cub Cadet zero-turn mower. More details on gas selection, ethanol’s deleterious effects, and fuel maintenance are provided.

SOLUTION: If you discover old gas in the fuel tank of your zero-turn, drain the tank with a fuel siphon pump. Put in new gas that has fuel stabilizer in it.

Sea Foam Motor Treatment is an excellent treatment for cleaning the fuel system and lowering moisture levels. You may get more information about it here.

Let the lawnmower run for a while to let the gas and fuel additive circulate. If you’re still having difficulties starting it, keep reading to learn about additional potential fuel-related causes.

5. Stuck Fuel Filter

A gasoline filter serves to remove debris from the fuel supply. An inline fuel filter installed in the gasoline lines will be used for your zero-turn vehicle. To prevent debris from getting into the carburetor and engine, it filters fuel as it’s being pumped from the tank.

When the fuel filter isn’t changed frequently enough, it can become clogged. The mower may turn over but fail to start if a sufficient amount of fuel cannot enter through the filter.

SOLUTION: Replace an old or unclean fuel filter with a new fuel filter.

6. Fuel Line Blockage

Then, move on to the carburetor by following the gasoline line from the tank. If the lawnmower cranks but won’t start, check for fuel flow restrictions.

Check for a gasoline limitation in the fuel line if you don’t discover any kinks. First, you’ll need to use gasoline pinch-off pliers or the fuel shut-off valve to stop the fuel from flowing.

After turning on the gasoline supply, check for sufficient flow by disconnecting the end of the line furthest from the tank and placing it in a container.

SOLUTION: If you aren’t getting enough fuel flowing via a fuel line, turn off the fuel source and disconnect the fuel line from the mower.

Put some carburetor cleaner in the line and spray it. This is done in an effort to break up the obstruction. The next step is to use compressed air to blow the obstruction out of the line. It may take multiple attempts with the carburetor cleaner and compressed air to clear the obstruction.

After the obstruction is cleared from the fuel line, reinstall it. If the restriction cannot be removed or if the gasoline line is old and showing signs of cracking, you should replace it.

7. Damaged Gasoline Pump

When the mower’s carburetor is situated beyond the height of the gasoline tank, a fuel pump is required. To get fuel to the carburetor at the top of the slope, the pump must struggle against the force of gravity.

The fuel pump on most zero-turns is a vacuum pump. This fuel pump design draws suction from the crankcase to prime the fuel injectors.

The gasoline pump must be replaced if it develops cracks or stops functioning properly. If there are no obvious signs of damage, such as cracks or gasoline leaks, you can still assess the fuel pump’s health.

It’s important to check that fuel is entering the pump’s inlet port before running any tests. (If not, perhaps there is something blocking the gasoline filter or fuel line.)

After checking that fuel is reaching the pump, you should disconnect the fuel line from the carburetor and store it safely. Start the gasoline flow and the mower to make sure the pump is working properly.

SOLUTION: The gasoline line should have a continuous or pulsing flow of fuel. If not, the fuel pump will need to be replaced.

Please consult your owner’s manual for fuel pressure requirements for different fuel pumps, such as electronic fuel injection pumps. If the fuel pressures are below the engine manufacturer’s recommended level, you should replace the fuel pump.

8. Bad Carburetor

The carburetor is a part of the engine that mixes fuel and air to create combustion. When the lawn mower’s carburetor breaks, it won’t turn over.

When a carburetor stops working, old gas is usually at blame. The varnish left behind by old gas can clog the fuel jet and make the engine’s internal parts stick.

SOLUTION: If the carburetor stops operating, you should clean it, replace any broken parts, or replace it with a new one.

Do this before you start dismantling the carburetor on your lawn mower:

  • Make sure the carburetor is getting sufficient fuel.
  • Get rid of the air filter.
  • Apply some carburetor cleaner to the mower’s air filter and turn it on. The carburetor is likely unclean if the engine starts, uses the carburetor cleaner, then runs poorly or shuts off after the cleaner is gone. *Starter fluid is not to be used.*
  • The carburetor should be taken apart, cleaned, or discarded and replaced. Here you will find information on how to clean the item.

9. Inadequate Fuel Cap/ Blocked Fuel Tank Vent

The fuel tank needs to vent so that the pressure inside the tank is the same as the outside. The gas cap of a lawnmower serves as the vent.

When the fuel tank’s vent is blocked, no air can escape through the cap, creating a vacuum. The absence of air around the carburetor prevents fuel from reaching it. Without petrol, the lawnmower will crank but not start.

SOLUTION: To see if your gas cap is the issue, loosen it and try to start the mower. The gas cap could be the problem if it fires up.

Let the mower run as you tighten the cap to be sure that’s the issue. If it sputters, turns off, and won’t restart unless you loosen the cap, you need to get a new one.

Read more: Cub Cadet Zero