How to Replace a Primer Bulb

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Last updated October 28, 2026 · Applies to: string trimmers from Toro, Husqvarna, Honda, Troy-Bilt, John Deere and Craftsman and others

Step 1: Identify the bulb type

Step-by-step instructions for this step are being written.

Primer and choke circuit: Fuel tank → Primer bulb → Return line → Carburetor → Choke plate → Run positionFuel tankpickup linePrimer bulbfills with fuel?Return lineback to tankCarburetorpriming portChoke plateclosed to startRun positionchoke open
Primer and choke circuit. A cracked primer bulb pushes air, not fuel. The choke must open once the engine fires.

Step 2: Remove the old bulb and retainer

Step-by-step instructions for this step are being written.

Primer and choke circuit: Fuel tank → Primer bulb → Return line → Carburetor → Choke plate → Run positionFuel tankpickup linePrimer bulbfills with fuel?Return lineback to tankCarburetorpriming portChoke plateclosed to startRun positionchoke open
Primer and choke circuit. A cracked primer bulb pushes air, not fuel. The choke must open once the engine fires.

Step 3: Fit the new bulb and lines

Step-by-step instructions for this step are being written.

Primer and choke circuit: Fuel tank → Primer bulb → Return line → Carburetor → Choke plate → Run positionFuel tankpickup linePrimer bulbfills with fuel?Return lineback to tankCarburetorpriming portChoke plateclosed to startRun positionchoke open
Primer and choke circuit. A cracked primer bulb pushes air, not fuel. The choke must open once the engine fires.

Step 4: Prime and test

Step-by-step instructions for this step are being written.

Primer and choke circuit: Fuel tank → Primer bulb → Return line → Carburetor → Choke plate → Run positionFuel tankpickup linePrimer bulbfills with fuel?Return lineback to tankCarburetorpriming portChoke plateclosed to startRun positionchoke open
Primer and choke circuit. A cracked primer bulb pushes air, not fuel. The choke must open once the engine fires.

Brand notes

Brand-specific notes for Toro, Husqvarna, Honda and Troy-Bilt are being researched.

When to take it to a shop

Hand it over if the engine still will not run after the fuel, spark and air checks, if you find metal in the oil or the engine is seized, or if the machine is under warranty (opening it yourself can void it).

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Frequently asked questions

Answers being written: Why is my primer bulb not filling with fuel? · Which fuel line goes to the primer bulb? · Are primer bulbs universal? · Can a cracked primer bulb stop an engine starting?