My Petrol Lawnmower Is Leaking Fuel from the Primer Bulb.

If fuel is leaking from the primer bulb on your lawnmower, this is usually caused by fuel backing up from the carburettor and escaping through the primer system.

Table of Contents

1. What Causes Primer Bulb Fuel Leaks?
2. The “Bleed & Tap” Procedure
3. Restarting the Machine
4. If the Problem Persists

What Causes Primer Bulb Fuel Leaks?

If fuel is coming out of the primer bulb, it typically indicates that:

• Fuel is overfilling the carburettor float chamber
• The float valve inside the carburettor is stuck open
• Fuel is being forced back through the primer line

In most cases, the issue is caused by a temporarily stuck float valve, which can often be resolved without replacing parts.

The “Bleed & Tap” Procedure

This simple procedure helps release pressure from the carburettor and free a stuck float valve.

Step 1 – Locate the Carburettor

Find the carburettor on the engine.

It is a metal component approximately the size of a fist, located between the air filter and the engine block.

Step 2 – Loosen the Float Chamber Nut

You will see two main nuts on the carburettor:

• One at the bottom
• One positioned at an angle (approximately 45°)

Using a suitable spanner, carefully loosen the angled nut.

Important: Do not fully remove the nut.

Step 3 – Bleed Excess Fuel

Allow fuel to drain from the loosened nut for approximately 20–30 seconds.

This relieves pressure and clears excess fuel from the carburettor chamber.

Step 4 – Re-Tighten the Nut

Once fuel has stopped draining:

• Retighten the angled nut securely
• Ensure it is properly sealed, but do not overtighten

Step 5 – Tap the Carburettor Float Chamber

Using a spanner, screwdriver handle, or similar tool:

• Gently tap the float chamber area of the carburettor a few times

This helps free the internal float valve if it is sticking.

Restarting the Machine

Once the procedure is complete:

1. Attempt to start the lawnmower as normal.
2. Prime the engine if required.
3. Check for any further fuel leakage from the primer bulb.