Brush Cutter Won’t Start? The Checks to Run, in the Right Order

This article contains affiliate links: if you buy through them, Wanda-techs earns a commission at no extra cost to you.

Your brush cutter won’t start, or it starts and stalls right away? Most often the starting procedure or the fuel is to blame. Check those first, before the spark plug and the filters.

Common symptoms and causes

• The engine doesn’t even cough: starting procedure not followed correctly (stop switch, choke, priming).
• The engine starts, then stalls: choke left halfway, old fuel or a wrong mix.
• The spark plug is wet after several pulls: flooded engine.
• The spark plug is dry: fuel isn’t reaching the cylinder.
• Hard starting and loss of power: clogged air filter.
• Cracked spark plug, or one covered in carbon or with worn electrodes.
• Clogged fuel filter, fuel line or carburetor.
• Blocked muffler spark arrestor, or a fuel cap whose vent is obstructed.

Battery-powered models are not covered by this guide: they have no spark plug, no fuel and no choke.

Before you start

• Let the engine and the muffler cool down before any work.
• Keep your model’s manual within reach: it gives the spark plug part number, the electrode gap and the fuel mix ratio.
• Have a spark plug wrench, a clean rag, gloves, eye protection and ear protection ready.
• For each attempt, set the machine flat on the ground with the cutting attachment clear of the ground and of any obstacle, and hold it firmly.

Warning: stop the engine and wait until the cutting attachment has fully stopped before any work. The spark plug makes the spark that ignites the gasoline: disconnect the spark plug boot (the cap that sits on the plug) before touching the engine, and never test for spark near gasoline vapors. Never start the machine in a garage or any enclosed space, because exhaust gases contain carbon monoxide.

Warning: opening the carburetor or the engine may void the warranty; check the warranty end date first. The carburetor, compression and the internal fuel filter are a job for an authorized repair shop.

Solution 1: start the brush cutter in the right order

The order of the steps differs depending on whether the engine is cold or warm. One missed step is enough to flood the engine.

Cold start

1. Set the stop switch to ON.
2. Press the primer bulb (the small soft bubble that sends fuel to the carburetor) until you see fuel inside it, about 5 presses according to Husqvarna Belgium; check your manual.
3. Set the choke (the flap that enriches the mixture when the engine is cold) to START.
4. Hold the machine firmly on the ground.
5. Pull the starter cord until the engine fires briefly or tries to start.
6. Move the choke to RUN.
7. Pull the starter cord again until the engine starts.
8. Let it idle for a few moments, then give it a short burst of throttle.

The engine should hold an idle on its own, with the choke on RUN.

Good to know: some models have a halfway choke position. The manual tells you when to use it.

If the brush cutter won’t start when warm

1. Check that the stop switch is on ON.
2. Leave the choke on RUN and don’t press the primer bulb, as manufacturers generally specify; follow your manual if it says otherwise.
3. Pull the starter cord until the engine starts.

The engine should restart without the choke. If it starts and then stalls, check that the choke is fully on RUN.

Warning: don’t keep pulling the starter cord without checking the choke position.

Solution 2: put in fresh fuel and the right mix

Fuel stored for too long can gum up the fuel system. On a 2-stroke engine, the oil is mixed with the gasoline in the tank, so the ratio matters.

1. Empty the tank.
2. Prepare a fresh mix at the ratio given in your model’s manual.
3. Fill the tank with this fresh fuel.
4. Loosen the fuel cap slightly.
5. Repeat the starting procedure from solution 1.
6. If the engine only starts with the cap loosened, clean or replace the cap.

The engine should start and keep a steady speed. Starting only with the cap loosened points to a blocked vent: the small opening that lets air into the tank as the level drops.

Pre-mixed 2-stroke fuel saves you from measuring the mix yourself. Use it if your model’s manual allows it.

Stihl MotoMix ready-mixed 2-stroke fuel

Alkylate fuel already mixed with 2-stroke oil at 1:50. It avoids mixing mistakes and keeps better than ordinary petrol.

• AmazonSee at Amazon

Good to know: a Stihl manual specifies a 1:50 mix, meaning 1 part 2-stroke oil to 50 parts gasoline. The ratio varies with the model and the oil. According to user reports, a mix that is too rich, at 3%, makes the engine stall.

Solution 3: flooded brush cutter, wet or dry spark plug

A flooded engine has received too much fuel to start. No official page we reviewed covers this case: the method below comes from user reports.

1. Disconnect the spark plug boot.
2. Unscrew the spark plug with the spark plug wrench.
3. Look at the tip of the plug: wet or dry.
4. If it is wet, dry it with a clean rag.
5. Let the cylinder air out with the plug removed; one user left it to dry overnight.
6. Screw the plug back in by hand, then tighten it with the wrench without overtightening.
7. Reconnect the spark plug boot.
8. Start with the choke on RUN, and don’t set the choke again for each attempt.

The engine should cough, then start. Next time you start it cold, switch the choke off at the first cough.

A dry plug while fuel reaches the carburetor points elsewhere, according to the same reports: the choke, hardened carburetor diaphragms or an air leak (air getting in where it shouldn’t). The diaphragms and the air leak are a shop job; check the spark plug and the filters first.

A spark plug wrench lets you remove and refit the plug without damaging its base.

AEG spark plug wrench, 3 sockets 14-16-21 mm

Spark plug wrench with three socket sizes. It removes and refits plugs without damaging the insulator.

• AmazonSee at Amazon

Solution 4: check and replace the spark plug

The spark plug wears out and gets covered in carbon, the black deposit left by combustion.

1. Disconnect the spark plug boot.
2. Unscrew the plug with the wrench.
3. Look for a crack in the plug.
4. Check the electrodes: thick carbon or worn tips.
5. If the plug is damaged, replace it with the part number from the manual, set to the correct gap.
6. Screw the plug in by hand, then tighten it with the wrench without overtightening.
7. Reconnect the spark plug boot and repeat the starting procedure.

The engine should start in fewer pulls than before.

Tip: a damaged spark plug is replaced, not cleaned.

Warning: the wrong spark plug or a wrong gap can damage the engine. Use the values from your manual, not those of another model.

If your manual lists this part number, here is an NGK spark plug to check before you buy.

NGK BPMR7A spark plug

Resistor spark plug for 2-stroke chainsaw and garden tool engines. It replaces a worn or fouled plug, provided the reference matches your manual.

• AmazonSee at Amazon

Solution 5: air filter, fuel filter and spark arrestor

A clogged air filter makes starting difficult and costs you power. Open its cover, then treat the filter according to its type.

1. Foam filter: wash it in warm soapy water.
2. Then apply a light film of filter oil to the foam.
3. Paper filter: tap it to knock the dust out, and never wash it.
4. Replace the filter if it is torn or very dirty.

Put the filter and its cover back. The spark arrestor is a screen on the muffler, behind a cover; not every model has one. Work with the muffler cold.

1. Remove the cover that protects the spark arrestor.
2. Look for a tear or a hole in the screen.
3. Brush off the carbon with a wire brush.

Refit the cover. The engine should start and rev up without struggling.

Good to know: Husqvarna advises cleaning the spark arrestor every 50 hours, and checking the screen every week on some models.

A clogged fuel filter, a blocked fuel line or a dirty carburetor also disrupt the fuel supply. Husqvarna leaves their replacement to an authorized dealer.

If nothing works

Stop if the engine still won’t start with fresh fuel, a new spark plug and a clean air filter. A carburetor that needs adjusting or repair, compression, the starter and worn internal parts are a job for a dealer or an authorized shop for the brand.

Have the make, model and serial number of the machine ready, plus the purchase date and a list of what you have already tried. The same reasoning applies to a chainsaw that won’t start, another 2-stroke engine, and to a lawn mower that refuses to start.

Take better care of your brushcutter: our toolbox

These products help the engine start more easily and protect both the engine and you.

Frequently asked questions

Why won’t my brush cutter start when it has gas?

The fuel may be too old, wrongly mixed or not reaching the engine. Fuel stored for too long can gum up the system, and a cap whose vent is obstructed disrupts the fuel flow. Also check the starting procedure, the spark plug and the air filter.

What should I do when the brush cutter’s spark plug is wet?

A wet plug after several pulls means too much fuel in the cylinder, according to user reports: the engine is flooded. Dry the plug, let the cylinder air out with the plug removed, then refit it. Restart with the choke on RUN, without setting it again for each attempt.

How do I start a flooded brush cutter?

Remove the spark plug, dry it with a clean rag and let the cylinder air out before refitting it. Then restart with the choke on RUN, without setting the choke again for each attempt. This method comes from user reports; no official page we reviewed covers this case.

Why won’t the brush cutter start when it’s warm?

When warm, the engine generally starts without priming or choke: leave the choke on RUN and pull the starter cord. If it starts and then stalls, check that the choke is fully on RUN. If the problem continues, check the spark plug, the air filter and the spark arrestor.

What fuel mix does a 2-stroke brush cutter need?

The ratio depends on the model and the oil used: the manual’s figure is the one to follow. A Stihl manual specifies 1:50, meaning 1 part 2-stroke oil to 50 parts gasoline. According to users, a mix that is too rich, at 3%, causes stalling.