Symptoms
- Pressing the primer bulb feels mushy, doesn't spring back, or has no resistance
- No fuel visible being drawn in through the bulb's line when pressed
- Bulb looks cracked, discolored, or brittle
- Mower is otherwise hard to start, especially when cold
Likely causes
- CommonCracked or brittle primer bulbRubber and plastic primer bulbs degrade with age and sun exposure, developing cracks that leak air instead of drawing fuel.
- PossibleClogged fuel line to the primerDebris or varnish can block the small line the primer uses to draw fuel.
- PossibleEmpty or very low fuel tankThere's simply not enough fuel for the primer to draw from.
- PossibleStuck check valve inside the primer assemblyA stuck valve can prevent the bulb from building the needed vacuum to prime the carburetor.
What to do
- Check the fuel tank level; a nearly empty tank won't let the primer draw fuel effectively.
- Inspect the primer bulb visually for cracks, tears, or a mushy feel that doesn't spring back.
- If cracked, most primer bulbs are inexpensive and can be pulled out and replaced without removing the whole carburetor.
- Check the small fuel line connected to the primer for clogs or damage.
- Replace the primer bulb, making sure it seats fully and forms a good seal in its housing.
- Test by pressing several times, feeling for it to spring back fully and see fuel begin to appear in the line, if visible.
Tools and parts
- Small flathead screwdriver or pick
Primer bulbSearch: “lawn mower primer bulb replacement”
When to call a pro
If a new primer bulb doesn't fix hard starting, the issue is likely elsewhere in the fuel system or carburetor, which a small engine shop can diagnose.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.