Small Engine Won't Start? Here's Your Diagnostic Flowchart

A small engine failure follows a pattern. No start. Weak start. Starts and stalls. Runs rough. If you know the pattern, you can diagnose it yourself in five minutes.

The Diagnostic Tree

Does it turn over at all? If no, the engine is seized. Pull hard five times. If still locked, bring it in.

Does spark plug have spark? Remove spark plug, hold against cylinder head, pull cord. See spark jump? If not, replace spark plug ($5-15). If no spark after replacement, ignition coil is bad ($80-150).

Is fuel getting to carburetor? Disconnect fuel line, turn petcock to on. Does fuel drip out? If not, tank empty or fuel line clogged. If fuel flows, carburetor is the problem.

Is carburetor flooded? Remove spark plug. Is tip wet with fuel? If yes, carburetor flooding. Pull cord 10 times to clear excess fuel. Reinstall fresh spark plug. If happens again, carburetor needs cleaning ($60-100).

Engine fires but stalls immediately? Check: Choke on or off? Cold engines need choke ON. Warm engines need choke OFF. If choke correct and still stalls, carburetor mixture is wrong. Bring it in ($35-50).

Engine runs rough, misfires, or dies under load? Replace spark plug ($5-15). Replace air filter ($15-30). Replace fuel filter ($10-20). Add fresh fuel ($0). If still rough, carburetor cleaning ($60-120).

The Four Quick Fixes That Solve 75% of Problems

1. Replace the spark plug ($5-15).
2. Replace the air filter ($15-30).
3. Replace the fuel filter ($10-20).
4. Drain old fuel, add fresh fuel with stabilizer ($0).

Do these four before calling a technician.

If still won't start: Professional diagnostic ($35) uncovers: carburetor clogged ($60-120), ignition coil bad ($80-150), fuel pump dead ($40-80), or compression loss ($200-500).

Call 301-519-9274 to schedule.

About the Author

Henry Bockman has diagnosed thousands of small engines over 37 years. This flowchart is based on real patterns he's seen.