Scag Mower Turns Over But Won’t Start

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Does your Scag mower turn over but just won’t start? This can be as a result of a bad spark plug or battery issue. 

In this article, I talk about the common reasons your Scag mower turns over but won’t start and also share troubleshooting tips to help you diagnose and fix this problem.

Reasons Why Your Scag Mower Turns Over But Won’t Start


The reasons your Scag mower turns over but won’t start may include:

  • Bad spark plug
  • Dirty air filter
  • Stale fuel
  • Fuel restrictions
  • Carburetor problems
  • Sheared flywheel key
  • Dead battery 

Tools You Need For This Job

Some tools you may need to have nearby when troubleshooting include:

  1. Work gloves
  2. Screwdriver
  3. Pliers
  4. Siphon
  5. Empty container 
  6. Multimeter
  7. Compressed air
  8. Carb cleaner
  9. Carburetor rebuild kit
  10. Clean rag

Scag Mower Turns Over But Won’t Start: Causes, Diagnosis, and Fixes

1. Bad Spark Plug 


The first thing you should check if your Scag mower turns over but won’t start is the spark plug

A worn-out or fouled spark plug on your Scag can cause the plug to fire irregularly or produce an insufficient spark, causing it to turn over but not start. 

In addition to being fouled, the spark plug may cause starting issues if it is not gapped correctly, if it is broken, or if the spark plug wire is not tightly connected.


Remove the plug wire and inspect the spark plug for signs of carbon build-up, burnt electrodes, rust, and wear.


Replace the worn-out spark plug and attach the plug wire firmly to the plug so that it is securely connected.

2. Dirty Air Filter 


If you have eliminated the spark plug, check the air filter next. For combustion to occur, your air filter must both allow the right amount of air into the engine and filter out any debris that could damage the engine.

When did you last check it? Perhaps it’s about time for a thorough cleaning. The dirt and dust it filters out can eventually impair its performance.

When this happens, less air than necessary will get through it and into the carburetor, which may cause your mower to turn over but not start.


Check the condition of the air filter by removing the air filter housing. It is clogged if it is filthy or oil-soaked. 


Clean or replace the air filter. 

Also, clean the air filter housing before installing the new filter to remove any residual dust or debris.

3. Stale Fuel 

Stale fuel in your Scag mower gas tank may be the reason your machine won’t start.

Fuel can begin to evaporate and lose some of its quality as soon as 30 days after purchase.

For how long has the fuel been in the tank? If it is more than 30 days, it might have gone stale. 

The engine will be unable to run with stale fuel because it has lost most of its qualities. This could cause your mower engine to die after starting.


Check the condition of the fuel in your fuel tank. If it has sticky or slimy residue, it is stale.


If you find the fuel in your Scag mower is stale, drain the fuel tank using a fuel siphon pump. 

Refill the tank with fresh fuel and add a fuel additive like Sea Foam Motor Treatment to stabilize the fuel, clean the fuel system and reduce moisture.

4. Fuel Restrictions

How is the fuel supply system working? Are you getting enough fuel to the carburetor? Ask yourself these questions if your Scag mower turns over but won’t start.

Examine your fuel supply systems for any jams or blockages. The fuel transported to the carburetor will be reduced greatly or even stopped if any of the fuel supply systems, such as the fuel lines, fuel filter, and pump, are not functioning properly.


Examine each fuel line, fuel filter, and fuel pump. Examine the fuel flow through the lines and filter. It is clogged if it is not flowing freely.


Replace blocked fuel lines or clean them by spraying carburetor cleaner into the line. After that, clear the line by blowing compressed air through it. 

If you are unable to remove the obstruction, install a new fuel line in its place.

Replace faulty fuel filters and fuel pumps. 

Note: Before replacing damaged fuel components, ensure that the fuel in the gas tank is not stale, as this will cause the problem to reoccur. If the fuel has been sitting for more than 30 days, it should be replaced.

5. Carburetor problems 

The performance of the carburetor can be hampered by varnish and deposits left behind by stale gas. 

To enable combustion to occur in the cylinder, the carburetor controls the amount of fuel that is combined with air. 

A dirty or damaged carburetor will be unable to perform its duty effectively and may cause starting issues in your Scag mower.


Check the carburetor jets and bowl for dirt and sticky residue. The presence of this indicates clogged parts.

Check the float, needle valve, diaphragm, and carburetor gasket to see if they are functioning effectively.


Clean with a carburetor cleaner or rebuild the carburetor using a carburetor rebuild kit, and replace any damaged part.

6. Sheared Flywheel Key 

A Scag mower engine’s inability to start or poor performance is frequently caused by a sheared flywheel key. 

This is brought on by running into a rock, stump, or other immovable objects.

The flywheel key breaks in half to protect the engine from getting damaged when the engine suddenly stops or hits an obstacle.

When the flywheel key gets damaged, the engine of your Scag mower may crank but refuse to start.


Take a look at the flywheel key. If it is broken or cracked, it may be the culprit.


Replace it if there are any indications of shearing or if you are unsure of its condition. It is easy and affordable.

7. Dead battery

A Scag mower with a low or dead battery may turn over but refuse to start. The battery works with the spark plug to power the engine and enables it to start.

A dead battery will send insufficient power and this may result in a no-start mower situation.


Use a multimeter to test the battery voltage. If it is less than 12 volts, the battery is low.


Recharge the battery. If the battery refuses to charge, some battery cells may be damaged.

In this case, you may need to replace the battery.


If your Scag mower turns over but doesn’t start, it may be due to: a bad spark plug, dirty air filter, stale fuel, fuel restrictions, carburetor problems, sheared flywheel key, or a dead battery.

To determine the root cause, carefully examine and troubleshoot the vital parts of your mower’s engine as mentioned in this article. Then, apply the recommended fixes.