Symptoms
- Engine dies as soon as the choke is opened
- Runs rough or surges with choke partially closed
- Worked normally before, especially before a period of storage
- Fuel may be old or the mower recently sat unused
Likely causes
- CommonPartially clogged carburetor jetA small restriction lets enough fuel through only when the choke compensates by richening the mixture.
- CommonStale fuelOld gas has lost some of its lighter, more flammable components, making a normal mixture too lean to sustain running.
- PossibleVacuum or intake leakA leak lets in extra unmetered air, leaning out the mixture unless the choke compensates.
- PossibleDirty fuel filterRestricted fuel flow can only keep up with the richer choke setting.
What to do
- Drain old fuel and refill with fresh gasoline; run a tank through before further diagnosis.
- Check any inline fuel filter and replace it if it looks dark or clogged.
- Inspect the air filter and intake area for a loose gasket or crack that could cause a vacuum leak.
- If the mower still needs choke after fresh fuel, the carburetor likely has partial blockage from varnish and needs cleaning.
- A carburetor cleaning kit or spray cleaner applied to accessible jets can sometimes clear light blockages.
- If cleaning doesn't help, a full carburetor rebuild or replacement may be needed.
Tools and parts
- Carburetor cleaner spray
- Screwdriver
Carburetor rebuild kitSearch: “small engine carburetor rebuild kit”
Inline fuel filterSearch: “small engine fuel filter”
When to call a pro
A gummed-up carburetor is a routine job for a small engine shop if home cleaning doesn't resolve it.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.