A SCAG zero-turn mower turns over but won’t start when there is a lack of air, fuel, or spark to form combustion.
This may be caused by a wrong choke setting, plugged air filter, clogged fuel filter, plugged fuel filter, faulty fuel pump, dirty carburetor, bad spark plug, or old fuel.
Always follow the safety precautions in the SCAG operator’s manual. This includes waiting for the engine to cool and removing the ignition key and spark plug wires prior to 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.
9 Reasons a SCAG Zero Turn Mower Turns Over But Won’t Start
Stuck Choke or Incorrect Choke Setting
The choke is a component that restricts the amount of air getting to the engine when engaged. This is needed when starting a cold engine.
A cold engine requires a high concentration of gas and less air to start. Once the engine warms, the choke lever must be adjusted to the off position so the engine gets more air and continues to run.
If you are starting a warm engine, the choke must be in the off position.
SOLUTION: When the choke lever is in the wrong position, your SCAG will have a hard time starting and may not start at all. Ensure the choke is in the on/closed position for a cold engine and off/open position for a warm engine.
If the choke is set correctly and you are still having airflow issues, check to make sure the choke plate is not stuck and the choke cable is moving freely. Use carburetor cleaner to help free a stuck choke plate and linkages.
If you find the cable is stretched or worn, replace it with a new choke cable.
Plugged Air Filter
Another item that can restrict airflow and keep your engine from starting after it turns over is the air filter. This filter is an important part used to keep dirt and debris from being pulled into the air intake causing wear and potential engine damage.
The air filter must be checked regularly. It must be cleaned or replaced to keep it in good condition. When the air filter becomes so plugged with dirt, it can prevent a good flow of air from passing through the filter.
I recommend starting each mowing season out with a new air filter and then cleaning it several times throughout the season. The air filter is an item you need to take time to check before operating your mower to ensure it is in good condition.
SOLUTION: Follow the instructions below to clean a SCAG paper air filter and foam pre-cleaner if your engine uses a pre-cleaner.
When you are unsure what type of filter is used on your mower and how to clean it, refer to your operator’s manual for additional information about your model.
You can find more information on air filters in Guide to Lawn Mower Air Filters: Differences & How to Clean Them.
Clean a SCAG Mower Paper Air Filter
- Remove the filter for the air filter housing. Be careful not to allow dirt to fall into the air intake.
- Use a clean dry rag to wipe out any dirt or debris left in the air filter housing.
- Tap your paper air filter against a solid surface to knock as much dirt out of the air filter as you can remove.
- Hold your paper filter up to a light source and look to see if you can see light shine through the element.
- Reuse a filter when you can see light.
- Replace the filter with a new one when you can’t see any light, the filter is extremely dirty or is damaged.
- Install and reattach the air filter cover. (If your mower uses a foam pre-filter, clean it using the instructions below and install it before attaching the filter cover).
Clean a SCAG Mower Foam Pre-Filter (If used on your mower. Some engines will use a different type of pre-filter).
Do not confuse this with a primary foam filter. A foam pre-filter is an extra filter used with a paper air filter to trap dirt. NEVER add oil to a pre-filter or you will damage the paper filter.
- Inspect the pre-filter. Replace it if you find any tears or if it has become brittle.
- Wash the foam filter with water and mild dish soap to remove dirt and oil.
- Rinse with water until the soap is removed and the water runs clear.
- Lay flat and allow to dry. Placing the filter outdoors in the sun will speed up the drying process.
- Once dry install the foam pre-filter with the paper primary filter and reattach the filter cover.
Dirty Spark Plug
Next, check the condition of the spark plugs. Remove a plug by using a 3/4″ or 5/8″ socket wrench. The size you need will depend on your engine model.
A spark plug that is damaged or very dirty can cause an intermittent or lack of spark. Without a spark, the engine won’t be able to start and run.
Things to look for in a bad spark plug are a dark-colored tip, a burnt electrode, or a broken porcelain. If you find any of these conditions, install a new spark plug.
SOLUTION: You can attempt to clean a plug that is in good condition and just a little dirty. Use a small wire brush to remove the carbon buildup.
Reinstall the spark plug after you ensure the electrode 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 by installing new spark plugs in your SCAG mower.
In case you don’t already know, gas doesn’t stay good forever. In fact, it will begin to break down as soon as 30 days after purchase.
Old gas leaves behind varnish and sticky deposits that cause fuel restrictions and component failures.
To ensure you are running the right gas through your mower, always purchase fresh gasoline and consume it within 30 days. Stay away from gas with high ethanol levels.
Use gasoline with a minimum 87-octane rating and a maximum 10% ethanol content. SCAG mowers with 4-cycle engines use gasoline. SCAG mowers with 2-cycle engines use a gas and oil mixture.
Read more about choosing the right type of gas for a 2-cycle or 4-cycle engine in This is the Type of Gas SCAG Lawn Mowers Use.
SOLUTION: If you find your mower has old gas in the fuel tank, drain the fuel tank using a fuel siphon pump.
Fill the tank with fresh fuel in addition to a fuel stabilizer like Sea Foam to help clean the fuel system and reduce moisture. Read more about the benefits of Sea Foam here.
If you are able to get the mower started, allow it 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.
Plugged Fuel Filter
You will find an inline fuel filter installed between the fuel lines on your mower. The filter is used to strain fuel that comes out of the fuel tank to keep dirt from flowing through the fuel system and to the engine.
The 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.
Clogged Fuel Line
Next, follow the fuel line from 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.
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 mowers use a vacuum fuel pump. This style of pump uses the vacuum of 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, ensure 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)
SOLUTION: 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.
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.
If your SCAG uses an electronic fuel injection pump, obtain a pressure reading using a fuel pressure gauge. 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.
The carburetor’s function is to mix gas with air to form combustion in the engine. When the carburetor fails to work, your engine will not start because it isn’t getting enough gas.
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 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 more detailed information for cleaning a carburetor here.
Plugged Fuel Vent in the Gas Cap
The fuel tank must vent to equalize the air pressure inside that tank to the atmospheric air pressure. On a SCAG 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.
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.
SOLUTION: Replace a bad or plugged gas cap with a new one.
Still Experiencing Problems with Your SCAG Lawn Mower?
Own a lawn mower long enough, you’ll start running into problems with it starting, not continuing to run, smoking, leaking gas, giving a bad cut, vibrating, or another issue.
To help you save time and money, I have put together a guide to help you troubleshoot the next problem that develops on your mower.
You can find this guide at Common SCAG Lawn Mower Problems & Solutions.
If you are unsure how to perform diagnostics and repairs on your lawn mower safely, it’s best to have a professional complete the repairs.
This will help you avoid personal injury or additional damage to the mower. Your local SCAG lawn mower dealership or lawn mower repair shop will be able to help you solve your problem.