ATV Cranks but Won't Start — Fuel, Spark, or Compression?
When an ATV spins over normally but refuses to fire, the engine has one of three problems: it's not getting fuel, not getting spark, or not building compression. All three present identically from the outside — a motor that spins but won't start. Distinguishing between them requires systematic testing. Assuming it's a fuel problem and adding carburetor cleaner doesn't help if the ignition coil has failed.
Common Symptoms
- Engine cranks (starter motor turns) but won't fire
- Occasionally starts but not reliably
- Backfires once or twice then stalls
- Engine starts cold but won't restart when hot
- Strong fuel smell — may be flooded
Likely Causes
- Carburetor clogged with old fuel residue — fuel delivery failure
- Fuel petcock stuck closed or degraded
- Failed ignition coil — no spark at plug
- Fouled or worn spark plug
- Stuck float in carburetor causing flooding
- Low compression from worn rings, valves, or head gasket
- Timing issue from stretched cam chain
What We Inspect
- Spark test at plug wire — is there spark, and is it strong?
- Fuel delivery — is fuel reaching the carburetor and past the needle and seat?
- Carburetor condition and jet cleanliness
- Compression test — is the engine building adequate compression?
- Spark plug condition — fouled, worn, or cracked
- Timing and cam chain tension where accessible
Professional Diagnosis
Pouring starter fluid into the intake or adding fuel additives is a diagnostic shortcut that can damage engines and often doesn't reveal the real cause. A proper diagnosis determines which of the three systems is failing before any parts are replaced.
Related service: ATV & UTV Repair