Is your lawn mower cranking but not starting? Does it sputter, run for a second, or fail to start at all—even though there’s gas in the tank? You might be facing one of the most common small engine problems: your mower isn’t getting gas where it’s needed. The good news? This guide will walk you through every cause and solution, so you can get your mower running again without a trip to the repair shop.
How Your Mower’s Fuel System Works (and Where It Can Fail)
The typical mower fuel system pulls gas from the tank, through a filter and fuel line, into the carburetor, where it mixes with air and flows into the engine. If gas isn’t reaching the carb or engine, your mower won’t start—or might die quickly after starting.
- Gas tank: Needs fresh, uncontaminated fuel and proper venting.
- Fuel filter: Prevents debris from reaching the carburetor, but can clog up over time.
- Fuel line: Carries fuel; can get blocked, kinked, or cracked.
- Fuel shutoff valve: Must be open to allow fuel flow.
- Carburetor: Mixes fuel and air. If dry, the fuel isn’t arriving—or the float/needle is stuck.
Common Signs Your Mower Isn’t Getting Gas
- Mower cranks but never starts, even with fresh fuel
- Runs only a few seconds on starting fluid, then dies
- Carburetor bowl is dry after repeated starting attempts
- Primer bulb doesn’t fill with fuel, or feels flat
- No fuel in the fuel filter (if clear type is used)
- No gasoline smell at the carburetor or air intake
1. Is There Fresh Fuel in the Tank?
It sounds basic, but always check first! Old gas breaks down, gums up the carb, and won’t burn properly.
- Empty out stale or bad-smelling gasoline; refill with fresh regular unleaded (E10 or lower if possible).
- Look for debris, water, or sediment at the bottom of the tank. Drain and clean if needed.
- If you hear a vacuum “whoosh” when opening the gas cap, the cap vent may be clogged—clean or replace the cap.
2. Check the Fuel Filter
The fuel filter is your mower’s first line of defense against gunk—but it’s also the first part to clog.
- Find the filter (usually in the line between tank and carburetor).
- If it’s dirty, dark, or won’t let fuel pass through, replace it.
- Try blowing through the filter. If it’s blocked, install a new one.
3. Inspect the Fuel Line for Kinks, Cracks, or Blockages
- Fuel lines get brittle with age. Look for cracks, bends, or mushy spots.
- Remove the line and blow through it. If blocked or weak, replace it with the same diameter hose.
- If the line collapses under suction (when the engine tries to draw fuel), it’s time for a new one.
4. Is the Fuel Shutoff Valve Open?
- Some mowers have a manual valve between the tank and carburetor. Double-check that it’s turned fully open.
- If the valve feels sticky or doesn’t flow fuel when open, remove and clean or replace it.
5. Check the Primer Bulb (If Equipped)
- Press the primer bulb. It should draw fuel into the carburetor and you may see fuel in the bulb or line.
- If the bulb stays flat, won’t spring back, or never draws fuel, it could be cracked, leaking, or the line may be blocked.
- Replace the primer bulb or any cracked lines as needed.
6. Test Fuel Flow to the Carburetor
- Turn off the fuel valve (if there is one).
- Disconnect the fuel line at the carburetor.
- Place the open end into a clear container.
- Turn on the fuel valve and watch for flow—gas should stream freely.
- If flow is weak or absent, the problem is upstream (filter, tank, line).
- If fuel flows freely but the carb bowl stays dry, the carburetor float or needle valve may be stuck closed.
7. Carburetor Problems: Float, Needle, and Jets
If fuel is reaching the carb but the bowl is still dry, a stuck float or needle valve may be blocking flow. Gummed-up jets or passages are also common if fuel sat for months.
- Tap the carburetor gently with a screwdriver handle to free a sticky float.
- Remove the bowl and check for debris, varnish, or stuck parts.
- Clean all jets and passages with carburetor cleaner and compressed air.
- Install a carburetor rebuild kit if the float or needle is worn or damaged.
8. Fuel Cap and Tank Venting Issues
A clogged fuel cap vent creates a vacuum in the tank, stopping gas flow. Try loosening the cap and starting the mower—if it fires up, the cap is the culprit.
- Clean or replace the fuel cap as needed.
- Make sure the small vent hole is open and clear.
9. Air Leaks and Vacuum Problems
Some mowers use vacuum to help draw fuel. Air leaks in gaskets or carb mounting surfaces can prevent fuel from reaching the engine.
- Check for missing or cracked gaskets at the carburetor base.
- Tighten bolts and replace gaskets if air leaks are found.
10. What If Fuel Gets to the Carb but the Engine Still Won’t Start?
- Check the spark plug for fouling, wear, or damage. Replace if needed.
- Inspect the air filter. If it’s dirty or clogged, replace it.
- If you smell fuel at the exhaust or plug is wet, you may have flooded the engine—see “How to Fix a Flooded Lawn Mower.”
- For older engines, low compression or internal problems can mimic fuel starvation.
Preventive Maintenance: Keep Fuel Flowing Strong
- Use fresh gasoline every season. Add fuel stabilizer if storing for more than 30 days.
- Replace the fuel filter and lines every 1–2 years, or at the first sign of wear.
- Clean the carburetor annually, especially after winter storage.
- Store the mower with the tank and carburetor empty if possible.
- Keep the tank and cap clean and debris-free.
Frequently Asked Questions (FAQ)
Why does my mower only run on starting fluid?
This means fuel isn’t reaching the carburetor—likely due to a blockage in the line, filter, or carb. Follow the steps above to find and clear the blockage.
How often should I change my mower’s fuel filter?
At least once per mowing season, or immediately if it’s dirty, dark, or slow-flowing.
Can a clogged air filter stop fuel from getting to the engine?
No, but it can make the engine run poorly or not start. The air filter doesn’t affect fuel delivery to the carb, but always check it when troubleshooting.
What fuel line size do I need?
Most walk-behind mowers use 1/4″ ID fuel line, but always check your manual for the exact size and type.
When should I call a professional?
If you’ve replaced fuel lines, filter, and cleaned the carb but the mower still won’t get gas—or if you find serious internal damage or leaks—it’s time to visit a repair shop.
Conclusion: Restore Fuel Flow and Get Back to Mowing
Most lawn mower “no gas” problems are solved by checking the basics: fresh fuel, clean filter, open lines, working primer, and a clear carburetor. With a methodical approach, you’ll quickly find the blockage and have your mower running strong again. Remember, a little regular maintenance keeps fuel delivery reliable season after season. For bigger repairs or repeated issues, don’t hesitate to reach out to a local small engine shop.
Don’t let fuel flow failures slow you down—keep your mower in top shape for a perfect lawn every time!