My Petrol Hedge Trimmer will not rev up

Quick Answer

If your petrol hedge trimmer starts and idles normally but will not accelerate, lacks power, or stalls when the throttle is applied, the cause is often stale fuel, a blocked air filter, restricted fuel flow, or incorrect carburettor settings. Follow the checks below before attempting any carburettor adjustments.

⚠️ Safety Notice

Before carrying out any maintenance or adjustments:

• Work in a well-ventilated area.
• Wear suitable protective equipment.
• Keep hands, clothing, and loose objects away from the cutting blades.
• Ensure the hedge trimmer is placed on a stable surface.

Carburettor adjustment should only be carried out by someone with the appropriate mechanical knowledge and the correct adjustment tool.

Why Won't My Hedge Trimmer Rev Up?

If the engine starts and idles correctly but struggles to accelerate or reach full speed, possible causes include:

• Old or incorrectly mixed fuel
• A blocked or dirty air filter
• Restricted fuel flow
• Incorrect carburettor adjustment
• A partially blocked fuel filter or carburettor

Carry out the following checks before adjusting the carburettor.

Preliminary Checks

Check the Fuel

Ensure the fuel is:

• Fresh
• Mixed to the correct ratio specified by the manufacturer
• Free from contamination

Old or incorrectly mixed fuel can reduce engine performance and prevent the engine from reaching full RPM.

Check the Air Filter

Inspect the air filter for dirt and debris.

A blocked air filter restricts airflow and can cause:

• Poor acceleration
• Reduced engine power
• Excessive exhaust smoke

Clean or replace the air filter if necessary.

Check the Fuel Cap

Ensure the fuel cap is correctly fitted and tightened by hand.

A loose or faulty fuel cap can affect fuel delivery and engine performance.

Carburettor Adjustment – High-Speed (H) Screw

If the preliminary checks have been completed and the hedge trimmer still will not rev up, the carburettor may require adjustment.

Important

⚠️ Incorrect carburettor adjustment can:

• Reduce engine performance
• Cause engine damage
• Increase exhaust emissions
• Invalidate your warranty

Tools Required

• Carburettor adjustment tool (Pacman type)

Step 1: Warm Up the Engine

Start the hedge trimmer and allow it to reach normal operating temperature.

Carburettor adjustments should always be made with a warm engine.

Step 2: Locate the Adjustment Screws

The carburettor contains the following adjustment screws:

Step 3: Check the Low-Speed Setting

Before adjusting the high-speed circuit, ensure:

• The engine idles smoothly.
• The engine does not stall.
• The cutting blades remain stationary at idle.

An incorrectly adjusted L screw can affect acceleration.

Step 4: Adjust the High-Speed (H) Screw

With the throttle fully open:

1. Turn the H screw anti-clockwise until the engine begins to lose maximum RPM.
2. Slowly turn the screw clockwise until the engine runs smoothly and reaches maximum RPM.
3. Test the throttle response.

The engine should accelerate cleanly without hesitation or stalling.

Avoid over-adjusting the H screw, as excessive engine speed can damage the engine.

If the Problem Persists

If the hedge trimmer still struggles to rev after completing these checks:

• Inspect the fuel filter for blockages.
• Check the spark plug for wear or carbon deposits.
• Ensure the exhaust spark arrestor (if fitted) is not blocked.
• Contact our Technical Support Team for further diagnosis.

Frequently Asked Questions

Why does my hedge trimmer idle but not rev up?

This is commonly caused by stale fuel, a blocked air filter, restricted fuel flow, or incorrect carburettor settings.

What does the H screw adjust?

The H (High Speed) screw controls the fuel mixture at high engine speeds and affects maximum RPM and acceleration.

Should I adjust the H screw before the L screw?

No. Always ensure the engine idles correctly before making any adjustments to the high-speed setting.

Can dirty fuel affect engine performance?

Yes. Old or contaminated fuel can restrict performance and prevent the engine from accelerating properly.

Can I adjust the carburettor myself?

Only if you have the correct adjustment tool and experience. Incorrect adjustments can damage the engine and may invalidate your warranty.