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String Trimmer Won’t Start When Hot (Troubleshoot 7 Reasons)

You were able to start and run your string trimmer for a while, but now that it shut down you can’t get it started again.

A string trimmer won’t start when hot due to a flooded engine, wrong choke setting, dirty carburetor, dirty spark plug, faulty ignition coil, plugged fuel tank vent, or vapor lock.

Follow the safety precautions provided in your string trimmer operator’s manual. Always remove the spark plug wire before making any repairs.

String trimmer won't start when hot

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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.

Your String Trimmer Won’t Start When Hot (SOLVED)

1. Engine Flooded / Wrong Starting Procedure

A choke lever is only engaged to restrict airflow so the fuel runs rich to start a cold engine. It is not needed when the engine is already warm.

Trying to start a warm engine with the choke lever in the closed position will not allow the engine to start.

Choke position to start a string trimmer:

  • Cold engine: start with the choke lever or knob in the closed position.
  • Warm engine: start with the choke lever or knob in the open position.

String trimmer engine is flooded:

When starting the engine, you may have flooded the engine so it won’t start. Here are a couple of common ways the engine is flooded:

  • The choke is closed and the starter rope is pulled too many times.
  • The on/off switch is off and the starter rope is pulled multiple times.
  • The primer bulb is pushed too many times. The primer bulb only needs to be pressed enough times that you just begin to see fuel in the bulb. The bulb does not need to be full.

This isn’t a serious problem and can be easily fixed using one of the options below.

SOLUTION: When starting an engine that is already hot, don’t engage the choke. Doing so will flood the engine allowing too much gas into the cylinder.

How to Fix a Flooded Engine on a String Trimmer – Option 1

  • Place the on/off switch in the on position.
  • Place the choke knob or lever in the open/run position.
  • Press the throttle lockout and squeeze the trigger while pulling the starter rope over and over. This can take anywhere between 5 and 15 pulls before it starts. Your string trimmer engine will sputter first. Continue to pull 2 to 3 more times and it should start.

How to Fix a Flooded Engine on a String Trimmer – Option 2

  • Place the switch in the stop/off position.
  • Remove the spark plug and clean it
  • Pull the starter rope 6 to 8 times.
  • Reinstall the clean dry spark plug.
  • Turn the switch to the start/on position.
  • Start the string trimmer with the choke off and in the open/run position.

2. Dirty Carburetor

The carburetor regulates the amount of gas that is mixed with the air required for your string trimmer to start and continue to run.

The passageways can become clogged and the small components can fail to function correctly which can be the reason the string trimmer stops running.

Old fuel is a big reason why a carburetor will stop working.

SOLUTION: You may be able to clean or rebuild your carburetor to get it working again. You will have to replace the carburetor if this doesn’t work.

3. Bad Spark Plug

A dirty or broken spark plug won’t provide the consistent spark needed to start and run a string trimmer. It may provide intermittent spark causing the saw to no longer start when hot.

SOLUTION: Inspect the condition of the spark plug tip. The spark plug must be replaced if it is very dark in color and has a broken porcelain or burnt electrode.

You can try to clean the spark plug with a wire brush and reuse it if it’s just a little dirty. I prefer to just replace it.

It’s an important part required for your string trimmer to start and run well. It’s also an inexpensive maintenance part.

Make sure the spark plug is gapped correctly and the spark plug wire is securely attached. (Don’t leave the spark plug attached if you need to continue to make additional repairs).

4. Faulty Ignition Coil

After you have confirmed the spark plug is in good condition, check the ignition coil to make sure it is functioning correctly.

The coil provides the electrical current to the spark plug to form a spark that ignites the fuel to start and keep your string trimmer running.

When the coil gets hot, the winding on the coil can separate and short out. This will cause your string trimmer to fail to start when there is intermittent or no spark.

A bad ignition coil will not be able to provide sufficient voltage to the spark plug.

SOLUTION: Test the ignition coil and replace it if you find there is a break in continuity.

5. Plugged Fuel Tank Vent

The fuel tank on a string trimmer must be able to vent to allow air to pass into the tank.

Air must be able to pass through the vent and out of the tank when fuel is added. Air also needs to be able to pass into the tank when the fuel level decreases.

When the tank isn’t able to vent, vacuum forms that will prevent fuel from leaving the fuel tank to flow to the carburetor. This will cause the string trimmer to die and not restart until the fuel tank is able to get air.

SOLUTION: Locate the fuel vent on your string trimmer and replace a clogged vent. It is a small circular part that is installed on the top side of the tank.

6. Vapor Lock

When the fuel mixture in a string trimmer heats up it may vaporize creating bubbles that interfere with fuel getting to the engine. The string trimmer may not start until it cools down.

SOLUTION: Allow the string trimmer to cool. To reduce vapor lock conditions, always use fresh fuel and air-cooled engine oil.

You are more likely to experience vapor lock when running the saw in very hot conditions and for extended periods.

Take caution removing the fuel cap. When the fuel tank is under pressure, fuel can spray out of the fuel tank when removing the cap.

7. Plugged Spark Arrestor

Most string trimmers use a spark arrestor. This is a small screen installed on the muffler to keep hot exhaust material from shooting out of the muffler.

This screen is used to protect the operator and to prevent debris from being ignited by this hot material causing fires.

The screen can become plugged with soot and prevent hot exhaust air from leaving the trimmer. This may cause your string trimmer to bog down and it may prevent it from starting.

SOLUTION: Disconnect the spark plug boot. Make sure your engine is not hot. Remove the engine cover and engine exhaust cover.

Remove the spark arrestor and clean it with a wire brush to remove the soot. If you are unable to sufficiently clean it or it has a hole in it or is damaged, you need to replace it with a new spark arrestor screen.

Need More Help With Your String Trimmer Starting Problem?

Check the quality of fuel. Old fuel can cause fuel restrictions and component failures that will keep the engine from getting the fuel it requires.

Read more about fuel, fuel restrictions, and other items that can result in starting problems with your string trimmer here.

Still Having Troubles With Your String Trimmer?

As the owner of a string trimmer, you’re going to run into problems with it occasionally. This is true of all trimmers no.

To help you quickly identify the cause of your problem and how to fix it, I’ve put together a handy reference guide. It includes information on what to do when your string trimmer stops running, won’t start, bogs down, and more.

You will find tables with problems and solutions to many common string trimmer issues along with links to information in more detail here.