Symptoms
- Engine won't start, or only runs with choke on
- Rough idle or surging RPM
- Stalls shortly after starting
- Fuel smells stale or the mower sat for a long period without stabilized fuel
Likely causes
- CommonVarnish deposits from old gasolineGasoline that evaporates in the carburetor leaves a sticky residue that blocks small jets and passages.
- PossibleDirt or debris in the fuelContaminated fuel or a torn fuel filter can introduce debris into the carburetor.
- PossibleStuck float or needle valveA stuck float can flood or starve the carburetor of fuel.
- Less commonDamaged carburetor gasketA leaking gasket can cause air/fuel imbalance mimicking a clog.
What to do
- Drain any old fuel from the tank and carburetor bowl before starting work.
- Remove the carburetor bowl (usually one bolt) and inspect for varnish, gunk, or debris.
- Spray carburetor cleaner through the accessible jets and passages, following the product's instructions.
- Check the float and needle valve for free movement and clean or replace if stuck.
- Reassemble with a new gasket if the old one is damaged or brittle, then refill with fresh gasoline.
- If cleaning doesn't restore normal running, a full carburetor rebuild kit or replacement carburetor may be needed.
Tools and parts
- Carburetor cleaner spray
- Basic wrench set
- Small brush
Carburetor rebuild kitSearch: “small engine carburetor rebuild kit”
Replacement carburetorSearch: “lawn mower carburetor replacement”
When to call a pro
If disassembly feels intimidating or cleaning doesn't fix it, a small engine shop can clean or replace the carburetor affordably.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.