When your lawn mower cranks but won’t start, or it fires for a second and dies, one of the most common causes is fuel not reaching the carburetor. This issue can happen on walk-behind, riding, and zero-turn mowers of all brands. Fuel delivery problems are almost always fixable at home—and diagnosing the cause can save you an expensive repair bill. This step-by-step guide covers every reason your mower’s carb isn’t getting gas, how to fix it, and how to prevent future problems.
How Your Mower’s Fuel System Works
- Gasoline is drawn from the tank through a filter
- It travels along a fuel line to the carburetor
- The carburetor mixes fuel and air, then delivers it to the engine
- If anything blocks the path from tank to carb, your mower won’t run
Signs Fuel Isn’t Getting to the Carburetor
- Mower cranks but won’t start, even with fresh gas
- Engine runs only a moment on starting fluid, then stalls
- No fuel in the carburetor bowl (remove the bowl to check)
- Primer bulb doesn’t fill, or stays flat when pressed
- Fuel filter or line appears empty
- No smell of gas at the carburetor intake
1. Is There Fresh Fuel in the Tank?
- Old or stale gas (older than 30 days) turns to varnish, clogs lines, and won’t run well
- Drain old gas, clean the tank, and add fresh fuel
- Look for signs of water or debris in the tank—condensation and dirt are common after storage
2. Check the Fuel Filter
- The filter is usually in the line between the tank and carburetor
- If dirty or filled with debris, it blocks fuel flow
- Try blowing through it—if air won’t pass, replace with a new filter
- Install the filter in the correct direction (arrow points to carburetor)
3. Inspect the Fuel Line
- Check for kinks, cracks, collapses, or blockages
- Remove the line and blow through it; it should be clear and easy to pass air
- Replace any line that’s soft, brittle, or blocked
- Ensure the hose connections are tight, with no leaks
4. Test the Fuel Flow to the Carburetor
- Turn off any fuel shutoff valve (if equipped)
- Disconnect the fuel line at the carburetor inlet
- Place the line in a clear cup or jar
- Turn the valve on or open the tank and watch—fuel should flow freely
- If flow is slow or absent, blockage is upstream (in the tank, line, filter, or shutoff valve)
- If fuel flows but the carb bowl remains empty, check the carburetor float and needle
5. Check the Fuel Shutoff Valve
- Some mowers have a manual valve between the tank and carb
- Be sure it’s fully open during operation
- If valve handle turns but no fuel flows, remove and clean or replace the valve
6. Inspect and Test the Primer Bulb (If Equipped)
- Primer bulbs should refill after pressing; if they stay flat or don’t fill, there’s a blockage or air leak
- Check primer lines for cracks or loose connections
- Replace cracked or brittle bulbs and lines as needed
7. Carburetor Issues: Float, Needle Valve, and Clogged Jets
- If the carburetor bowl is dry even with fuel present at the inlet, the float or needle valve may be stuck closed
- Gently tap the carb with a screwdriver handle to free a stuck float
- Remove the bowl and inspect for varnish, debris, or gummed-up parts
- Clean the carburetor with carb cleaner and compressed air
- If the float or needle is damaged, install a rebuild kit
8. Fuel Cap Not Venting
- If the gas cap’s vent hole is blocked, a vacuum forms in the tank and stops fuel flow
- Try starting the mower with the cap loose—if it runs, clean or replace the cap
- A “whoosh” sound when removing the cap is a sign of vent blockage
9. Air Leaks and Vacuum Problems
- Some mowers use engine vacuum to help draw fuel
- Check for missing or cracked carburetor gaskets and loose mounting bolts
- Replace gaskets if air leaks are found
10. Less Common Problems
- Debris or insects in the fuel tank pickup tube
- Rodent damage to fuel lines or primer hoses (especially after winter storage)
- Internal fuel pump failure (on some riding mowers and zero-turns)
Prevention: Keep Fuel Flowing Strong
- Use only fresh gas and add stabilizer if storing more than a month
- Replace fuel filters and lines every 1–2 seasons, or if you notice wear
- Run the engine dry or drain fuel before winter storage
- Check the gas cap vent and clean the tank every season
- Keep the deck, tank, and fuel cap area clean to avoid dirt contamination
Frequently Asked Questions (FAQ)
Why does my mower run on starting fluid but not gas?
This means fuel isn’t reaching the carburetor—often due to a clogged filter, blocked line, stuck float/needle, or bad cap vent. Work through the checklist above to find the problem.
How do I know if my fuel filter is clogged?
If you can’t blow air through it easily, or the filter looks dark or dirty, replace it. Clear filters may show air bubbles or an empty line when blocked.
Can a blocked gas cap really stop fuel flow?
Yes—a blocked vent in the gas cap will create a vacuum in the tank, preventing fuel from reaching the carburetor.
How do I clean a stuck carburetor float or needle?
Remove the carb bowl and gently free the float. Clean with carburetor cleaner, and install a rebuild kit if parts are worn or damaged.
Should I replace fuel lines and filter every year?
Replace at least every 1–2 seasons, or if you see cracks, leaks, or blockage. Always use ethanol-safe parts.
Conclusion: Restore Fuel Flow and Get Back to Mowing
A mower that isn’t getting fuel to the carburetor can usually be fixed quickly—by checking for fresh gas, clearing the lines and filter, inspecting the carburetor, and ensuring the tank is venting properly. With regular maintenance, you’ll keep your mower starting and running strong every season. If you get stuck, most local small engine shops can diagnose fuel delivery issues and help you get back to a healthy, green lawn.
Fix the flow—your mower (and your yard) will thank you!