My Petrol Hedge Trimmer will not idle

If your petrol hedge trimmer starts but stalls or cuts out when the throttle trigger is released, the engine may not be idling correctly.

This guide covers the basic checks you can perform before considering carburettor adjustment or repair.

Table of Contents

1. Preliminary Checks
2. Carburettor Adjustment – Low Speed (L) Screw
3. Unable to Perform This Procedure?

Preliminary Checks

Before adjusting the carburettor, ensure the following checks have been completed:

Fuel

Ensure the fuel is fresh and mixed correctly according to the manufacturer's recommendations.

Old or incorrectly mixed fuel can cause poor engine performance and prevent the machine from idling correctly.

Air Filter

Inspect the air filter and ensure it is clean and free from debris.

A blocked air filter can restrict airflow and affect the engine's idle speed.

Fuel Cap

Check that the fuel cap is fitted correctly and tightened by hand.

The cap should be secure but not overtightened.

Carburettor

If the above checks have been completed and the problem persists, the carburettor settings may require adjustment.

Carburettor Adjustment – Low Speed (L) Screw

Important: Carburettor adjustment requires a good level of mechanical knowledge. Incorrect adjustment may worsen the issue or cause engine damage.

Tools Required

• Carburettor adjustment tool ("Pacman" type)

Step 1 – Warm Up the Engine

Start the hedge trimmer and allow it to run until it reaches normal operating temperature.

Step 2 – Locate the Adjustment Screws

The carburettor has two adjustment screws:

• L (Low Speed) – Controls idle and low-speed operation.
• H (High Speed) – Controls maximum engine speed.

Step 3 – Adjust the Low-Speed (L) Screw

Carefully adjust the L screw until the engine idles smoothly without stalling.

The engine should tick over comfortably while the cutting blades remain stationary.

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

With the machine running at full throttle:

1. Turn the H screw anti-clockwise until the engine begins to struggle to reach maximum RPM.
2. Slowly turn the screw clockwise until the engine returns to maximum RPM and runs smoothly.

Once completed, release the throttle and check that the machine returns to a stable idle speed.

Unable to Perform This Procedure?

If you are not confident carrying out carburettor adjustments, we recommend that you do not proceed.

Attempting to dismantle or adjust components incorrectly may invalidate your warranty and could result in further damage.