Brushcutter won't start: 6 causes and solutions

Method first

A brushcutter that refuses to start is frustrating — especially when the grass grows faster than you can cut it. But a 2-stroke engine is simple: it needs a spark, fuel, and compression. If one of the three is missing, it won't start.

Follow this checklist in order — from simplest to most complex.

Cause 1: The spark plug

This is the first thing to check. Always.

Symptom: the pull cord operates normally, but no ignition, no sign of life.

Test: 1. Remove the spark plug (usually 19 mm wrench) 2. Inspect the electrode: black and fouled = too rich mixture or tired plug. White = too lean. Light brown = perfect 3. Test for spark: reconnect the plug wire, place the plug against the engine metal (ground), pull the cord. You should see a clear blue spark

Fix: clean or replace the plug. For most brushcutters, it's an NGK CMR6H or Bosch USR7AC. Budget: 3-5 euros. Change it at least once per season.

Cause 2: The air filter

A clogged air filter prevents the engine from breathing. On a 2-stroke, it happens fast — a few hours in dry grass is enough.

Symptom: engine coughs, smokes black, or won't rev up.

Test: remove the filter and try starting without it (just for testing — never run without a filter). If it starts, the filter is clogged.

Fix: clean the filter (compressed air or soapy water for foam filters) or replace it. Budget: 5-10 euros.

Cause 3: Stale 2-stroke fuel mix

The petrol/oil mix has a limited shelf life. After 30 days, the petrol starts to degrade (light components evaporate). After 60-90 days, the mix may become unable to start the engine.

Symptom: the engine ran fine last time, but after several weeks/months of rest, it refuses to start.

Fix: drain the old mix, rinse the tank, refill with fresh mix at the correct ratio (usually 50:1 = 20 mL of oil per liter of petrol). Use fresh fuel (premium unleaded, avoid high-ethanol blends if possible).

Cause 4: Clogged carburetor

If the fuel mix sat in the carburetor for a long time, varnish deposits clog the microscopic jets. This is the #1 cause of start-of-season starting failures.

Symptom: the engine tries to start (a few pops) but won't sustain. Or no reaction at all despite a clean plug and fresh fuel.

Carburetor diaphragm kit: 8-15 euros depending on brand. It's the most common repair kit for small 2-strokes.

Cause 5: The primer bulb

The small primer bulb must be pressed 5-8 times before a cold start. If the bulb is cracked or the priming circuit leaks, fuel doesn't reach the carburetor.

Symptom: when you press the bulb, it doesn't fill with fuel, or fuel isn't visible in the clear return line.

Fix: replace the primer bulb (clipped or screwed in). Also check the fuel lines: a punctured or disconnected line prevents priming. Bulb budget: 3-8 euros.

Cause 6: The ignition coil

If you have no spark despite a new plug, the problem is likely the coil (ignition module).

Symptom: no spark, new plug, intact wire.

Test: check the air gap between the coil and the flywheel magnets. The gap should be 0.3-0.4 mm (a business card works as a spacer). If the gap is correct and there's still no spark, the coil is dead.

Fix: coil replacement. Budget: 15-40 euros depending on brand.

The mechanic's tip

If you store your brushcutter for more than 30 days, drain the fuel from the tank AND run the engine until it stalls (to empty the carburetor). This is the best prevention against 80% of starting problems.

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