Why Your Engine Won’t Start at All
When a small engine refuses to start, the cause is almost always fuel, spark, air, compression, or a safety interlock. This guide walks you through the highest‑probability failures first so you can diagnose the issue quickly.
1. Empty Tank or Bad Fuel
Old gasoline loses volatility in as little as 30 days. If the engine hasn’t been run recently, start by draining the tank and adding fresh fuel. Ethanol blends can also cause moisture buildup and clogged jets.
For more help understanding symptoms tied to fuel issues, visit the Symptoms Index.
External reference: EPA Gasoline Basics
2. No Spark at the Plug
A fouled, cracked, or carbon‑coated spark plug will prevent ignition. Remove the plug, inspect it, and test for spark. If there’s no spark, replace the plug and re-test.
Internal link: FAQ page for common spark plug questions.
3. Carburetor Not Delivering Fuel
If the carburetor bowl is dry or the engine only runs on starter fluid, the carburetor is clogged. Ethanol deposits and varnish are the most common causes. Cleaning the main jet and float needle usually restores operation.
Internal link: Start Here for basic maintenance steps.
4. Safety Switch Preventing Start
Many mowers and equipment include seat switches, blade switches, and brake interlocks. If any switch fails or is not fully engaged, the engine will not crank or fire.
5. Low Compression
Engines with worn rings, blown head gaskets, or valve issues may not generate enough compression to ignite fuel. A compression test will confirm this.
6. Dead Battery or Bad Starter (Electric Start Models)
If the engine doesn’t crank at all, check the battery voltage and starter solenoid. Corroded terminals can also prevent power flow.
When to Seek Professional Help
If you’ve checked fuel, spark, carburetion, and safety switches and the engine still won’t start, a deeper mechanical issue may be present. A technician can perform leak-down testing and advanced diagnostics.