You’re still able to keep your mower running, but you have to engage the choke to do so. Running a mower with the choke on indicates you have an underlying problem that must be fixed before it potentially becomes a major problem.
A Cub Cadet only runs with the choke on when the engine is getting too much air or not enough fuel.
This may be due to a dirty carburetor; old gas; plugged fuel filter; faulty fuel pump; bad gas cap; clogged or punctured fuel line, or bad carburetor gasket.
Refer to your Cub Cadet operator’s manual for all safety precautions. This includes removing the ignition key and the spark plug boot prior to making repairs.
Reasons your Cub Cadet mower only runs with the choke on:
- Lack of fuel
- Old gas
- Dirty carburetor
- Clogged fuel line
- Bad fuel pump
- Plugged fuel filter
- Bad fuel cap
- Too much air
- Bad carburetor gasket
- Puncture in the fuel line
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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.
7 Reasons a Cub Cadet Only Runs With the Choke On Or Half On
Old Gas
Gas can become old and begin to degrade as soon as 30 days after purchase. The ethanol used in most gas has negative effects on the Cub Cadet small engine.
Ethanol attracts moisture to the fuel system. This water and ethanol mixture not only leaves behind varnish and deposits that restrict fuel but it is also corrosive.
Because of this, it is important to choose the right gas and consume it quickly.
Cub Cadet mowers require unleaded gasoline with a minimum 87-octane rating and maximum ethanol content of 10%. Never use gas that contains more than 10% ethanol.
Read more about selecting the right gas for your Cub Cadet here.
SOLUTION: Drain old gas from the fuel tank. Add fresh gas with a fuel additive mixed in to help clean the fuel system and reduce moisture.
I like to use Sea Foam Motor Treatment. You can read more about the advantages of Sea Foam on your fuel system and engine here.
Puncture or Clog
A puncture in the fuel line can cause air to be sucked into the line so the engine receives too much air. Or, a clog can develop in the line that restricts the amount of fuel the engine receives.
Either one of these issues can cause the mower to only run when the choke is on when the choke needs to be used to adjust the air getting to the engine to control the right fuel-to-air ratio needed for combustion.
SOLUTION: Inspect the fuel lines. Follow the line coming out of the fuel line and follow it up to the carburetor. Look for punctures or cracks that can introduce air to the fuel system.
Next, check for a clog in the fuel line that can restrict fuel. First, shut off the fuel flow using the fuel shut-off valve. Then remove the end of a section of the fuel line and place it in a container to collect fuel.
Turn the fuel flow back on and watch for good flow coming out of the fuel line and into the container. If you are not getting good flow, shut off the fuel supply and remove the fuel line from your Cub Cadet.
Spray carburetor cleaner into the line to loosen the clog. Follow this with compressed air to remove the clog. Repeat as necessary.
If you just can’t get the fuel line clean and the clog removed or you find a puncture, replace it with a new section of the fuel line with the same diameter.
Plugged Fuel Filter
The fuel filter is a small part that is placed between the fuel lines to keep dirt and other contaminants out of the fuel system causing wear on the engine.
This is a part that should be replaced annually to keep it in good condition. When it becomes plugged, the amount of fuel that is able to pass through the filter may be restricted.
A reduced amount of fuel may require the choke to be used to correct the ratio of fuel to air required for combustion.
SOLUTION: Remove the fuel filter and insert a new inline fuel filter between the fuel lines. You should find an arrow on the side of the filter housing.
The filter must be inserted so the arrow is placed in the direction of the fuel flow.
Faulty Fuel Pump
A fuel pump is used on your Cub Cadet if the carburetor is placed higher than the fuel tank. Most mowers use a vacuum pump that uses the vacuum off the engine to move fuel from the fuel tank to the carburetor.
To check the fuel pump, you need to confirm the pump is getting fuel to the inlet port. Then remove the fuel line from the carburetor and place it in a container to collect fuel as you test the flow coming out of the line.
SOLUTION: If you aren’t getting sufficient fuel flow or find any cracks or fuel leaks, replace the fuel pump with a new one.
Bad Carburetor Gasket
The gasket that sits behind the Cub Cadet carburetor can deteriorate over time. When this happens, it no longer seals properly and allows additional air into the system causing the engine to run lean.
Running lean is when there is a higher concentration of air and less fuel than required by the engine. The choke will need to be on to compensate for the extra air being pulled into the engine through a bad carburetor gasket.
SOLUTION: Gain access to the carburetor and carefully remove the linkages and bolts attaching the carburetor. Remove the carburetor and gasket.
Reinstall a new gasket and reattach the carburetor, bolt, and linkages. This is also a good time to determine if you need to clean the carburetor when you have it off the mower.
Dirty Carburetor
A carburetor is needed to regulate the amount of gas that is mixed with air for combustion. When it becomes dirty, most likely due to old gas, fuel passageways, and internal parts can become clogged and fail to function.
The carburetor will need to be cleaned or replaced so the engine can get the right amount of fuel to run well.
SOLUTION: If you are a little mechanical and don’t mind working with small parts, you should be able to remove and clean the Cub Cadet carburetor yourself following these instructions.
If the carburetor doesn’t work right after you clean it, you may have to rebuild it or replace it.
Bring your mower to a small engine dealer to have cleaned if you don’t want to tackle the job.
Bad Gas Cap
The fuel tank on a Cub Cadet mower must be able to vent allowing air to enter the tank as fuel is being consumed. When it isn’t able to vent, a vacuum will form in the fuel tank.
This will keep fuel from flowing out of the tank and getting to the carburetor.
On a Cub Cadet, the fuel tank vents through the gas cap. When the cap is broken or plugged, it must be replaced.
SOLUTION: You can try to identify whether the gas cap is bad by loosening the cap to allow air to get into the tank. If you are able to remove the choke and the engine continues to run, the cap may be bad.
Try to replicate the problem to further confirm the cap is bad. Tighten the cap while allowing the engine to run.
If it begins to run sluggish and you have to engage the choke to keep it running, but you can remove the choke when the cap is loosened, the cap is most likely the problem. Replace a bad cap.
Still Having Problems with Your Cub Cadet Mower?
If these tips haven’t solved your problem or if you are experiencing a different problem with your mower, check out my guide showing the most common issues and solutions: Common Cub Cadet Problems.
Here you’ll find the causes of issues like the mower not starting, a bad cut, a vibration, or a smoking problem. I include solutions along with links to more in-depth information.