ATV Won't Run After Sitting — Old Gas and Varnished Fuel System
Ethanol-blend gasoline begins to degrade within 30 days and can leave varnish and gum deposits throughout a fuel system within a season of sitting. An ATV that was running fine when parked in the fall may not start in the spring, or may run rough and cut out under load. This isn't a simple matter of adding fresh gas — the old fuel residue needs to be physically removed.
Common Symptoms
- ATV ran fine when parked but won't start after sitting
- Starts but runs rough, surges, or dies under load
- Runs on choke but dies when choke is opened
- Strong stale fuel smell from carburetor area
- Black or gummy deposits visible in the fuel bowl when removed
Likely Causes
- Varnished carburetor main jet — partially or fully blocked
- Stuck float — fuel won't enter the carburetor properly
- Gummed fuel petcock — not flowing correctly
- Degraded fuel lines with cracked or spongy walls
- Rust or sediment in the fuel tank
What We Inspect
- Carburetor disassembly — float, needle, jets, emulsion tube
- Fuel petcock flow and valve condition
- Fuel line condition — cracks, softening, kinking
- Fuel tank interior for rust and sediment
- Air filter condition — often clogged on stored machines
Professional Diagnosis
Fuel additives and carb spray can sometimes get a badly gummed carburetor running temporarily, but the deposits remain. Proper carburetor cleaning requires disassembly, solvent cleaning of every passage and jet, and inspection of the float and needle. We do this correctly so the problem doesn't come back mid-season.
Related service: Carburetor & Fuel-System Service