Symptoms
- Engine fires up then quits within a few seconds
- Restarting works briefly then dies again
- Runs longer with choke partially closed
- Sputters before stalling
Likely causes
- CommonClogged carburetor jetVarnish from old gas blocks the tiny fuel passage that keeps the engine running past initial start.
- CommonBlocked fuel cap ventA clogged vent creates a vacuum in the tank that starves the engine after a few seconds.
- PossibleDirty air filterRestricted airflow makes the mixture too rich and chokes the engine out.
- PossibleWater in the fuelWater separates and blocks smooth fuel flow, causing stall-and-restart cycles.
- PossibleChoke stuck partially closedAn overly rich mixture from a stuck choke floods the engine after starting.
What to do
- Loosen the fuel cap and try starting the mower; if it now runs longer, the cap vent is clogged and needs cleaning or replacing.
- Check the air filter and clean or replace it if it's dark, torn, or oily.
- Move the choke to the run position once warm; if it only runs with choke on, the carburetor likely needs cleaning.
- Drain the fuel tank if the gas looks cloudy or has been sitting all winter, and refill with fresh gasoline.
- Inspect the fuel line for cracks or kinks that restrict flow.
- If the problem persists, the carburetor bowl and jets likely need a cleaning, which is best done by a small engine technician if you're not comfortable disassembling it.
Tools and parts
- Replacement air filter
- Fresh gasoline
- Basic wrench set
Small engine air filterSearch: “lawn mower air filter replacement”
Carburetor cleanerSearch: “small engine carburetor cleaner spray”
When to call a pro
If cleaning the filter and fuel doesn't help, a shop can clean or rebuild the carburetor.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.