Small Engine Mechanic how-to
How to Diagnose an Engine That Won’t Start
Every engine needs fuel, spark and compression. Test them in order.
Quick answer
Every engine needs fuel, spark and compression. Test them in order. In short: check; remove; check, then complete the remaining steps below.
Step by step
Check the obvious: fuel in the tank, choke position and safety switches.
Remove the spark plug and test for spark with a spark tester.
Check fuel delivery to the carburetor and look for stale fuel.
Spray a small amount of starting fluid; if it fires briefly, suspect fuel.
Check compression with a gauge.
Repair the failed system and test run.
Safety reminders for small engine mechanics
- Disconnect spark plug wires or batteries before working on blades
- Drain fuel and work in ventilated areas away from sparks
- Wear eye protection when grinding and using compressed air
- Run engines only with exhaust vented outside
Key terms
Two-stroke engine · Four-stroke engine · Carburetor · Choke · Ignition coil · Flywheel key: see the full small engine mechanic glossary.