If your lawn mower isn’t priming—meaning, you press the primer bulb but no fuel gets to the carburetor—starting the mower can be nearly impossible. Priming is essential for cold starts, especially after storage or when temperatures drop. Here’s how to quickly diagnose why your mower won’t prime, what to check, and how to fix it for reliable starts every time.
Quick Picks: Most Common Reasons a Lawn Mower Won’t Prime
- Cracked or Hard Primer Bulb: A damaged bulb won’t draw fuel.
- Loose or Disconnected Primer Line: Primer hoses can crack, pop off, or split.
- Clogged or Dirty Carburetor: Fuel can’t move if the carb jets or passages are blocked.
- Empty or Old Fuel Tank: No fuel (or bad gas) means nothing for the primer to draw.
- Clogged Fuel Filter: A dirty filter blocks fuel flow to the primer and carburetor.
- Bulb Installed Incorrectly: An improperly seated or aftermarket bulb may leak air or fuel.
- Faulty Primer Assembly: Worn-out check valves or internal leaks mean the primer won’t pull fuel.
Buyer’s Guide: What You’ll Need to Diagnose & Repair
- Replacement primer bulb and hoses: Always get the right type for your mower model.
- Screwdriver set: For bulb, hose, and air filter access.
- Socket wrench set: For carburetor and fuel line removal.
- Carburetor cleaner spray: For clearing jets and passages.
- New fuel filter: Replace if clogged or dirty.
- Fresh gasoline: Old gas is a common culprit.
- Work gloves & safety glasses: For safe repairs.
Step-by-Step Guide: How to Fix a Lawn Mower That Won’t Prime
1. Inspect the Primer Bulb
- Check for cracks, hardening, or fuel leaks. A good bulb should feel soft and return after pressing.
- If damaged, brittle, or leaking, replace the bulb with an exact match.
2. Examine Primer Hoses
- Look for kinks, splits, or loose connections at both the bulb and carburetor ends.
- Replace any cracked or loose primer lines for a tight seal.
3. Check the Fuel Supply
- Make sure there’s fresh, clean fuel in the tank.
- Inspect the fuel filter and replace it if it’s dirty or looks clogged.
- If you see bubbles or air pockets in the lines, the system may be sucking air from a bad hose or loose connection.
4. Clean the Carburetor
- If fuel isn’t reaching the carburetor, a clogged jet or passage may be blocking the flow.
- Remove the air filter and spray carburetor cleaner into the intake and primer line port.
- If problems persist, remove and deep clean or rebuild the carburetor.
5. Ensure Proper Bulb Installation
- Make sure the new or replacement bulb is seated firmly and facing the right direction.
- Some bulbs are directional—follow your owner’s manual for correct installation.
6. Check for Faulty Primer Assembly
- If you’ve replaced the bulb and hoses but still can’t prime, the check valve inside the primer assembly may be faulty.
- Replace the entire primer assembly if it’s not holding pressure or drawing fuel.
Comparison Table: Lawn Mower Priming Problems & Solutions
| Problem | Solution | Difficulty | Parts Needed |
|---|---|---|---|
| Cracked Primer Bulb | Replace bulb | Easy | Primer bulb |
| Broken/Loose Hose | Replace hose | Easy | Primer hose |
| Clogged Carburetor | Clean or rebuild carb | Medium | Carb cleaner |
| Empty/Old Fuel | Refill with fresh gas | Easy | Gasoline |
| Clogged Fuel Filter | Replace filter | Easy | Fuel filter |
| Improper Bulb Installation | Reseat/replace bulb | Easy | Primer bulb |
| Bad Primer Assembly | Replace assembly | Medium | Primer assembly |
Frequently Asked Questions
How do I know if my primer bulb is working?
When pressed, you should feel resistance, see fuel move in the line (if visible), and sometimes hear a light “squish” as fuel enters the carburetor.
Can I use my mower without priming?
Most mowers need priming for cold starts. Without it, you’ll have a very hard time starting the engine after storage or on cold days.
Why does my new primer bulb still not work?
If a new bulb won’t draw fuel, check for leaks in the lines, a clogged carburetor, or a faulty primer assembly. All parts must seal tightly for proper priming.
How often should I replace primer bulbs and hoses?
Inspect yearly and replace any parts that are hard, cracked, or leaking. Sun and gas exposure cause these rubber parts to degrade over time.
What if nothing fixes the priming issue?
If you’ve replaced the bulb, hoses, and cleaned the carb but still can’t prime, consult a small engine repair shop—rarely, deeper carb or tank problems may be to blame.
Conclusion
If your lawn mower won’t prime, start by checking the primer bulb and hoses, then work your way through the fuel system for blockages or leaks. Most fixes are quick and affordable, and regular inspection of these small parts ensures your mower starts up every time—no matter the weather or season!