Won't Start
Briggs 450e Won't Prime or Stay Running
Updated 2026-05-20
A push-mower troubleshooting guide for Briggs & Stratton 450e engines with primer, fuel filter, air filter, carburetor, and spark plug lookup steps.
Primer System Checks
If the primer bulb does not move fuel or the mower only runs for a second, inspect the bulb, gasket surfaces, and carburetor pickup path.
A cracked primer bulb can create an air leak that looks like a dirty carburetor.
Air Filter and Carburetor
A plugged paper filter can make the engine run rich, while a blocked carb jet can make it surge or stall under load.
Match the engine code and carburetor number because mower brands often use the same engine family with small application differences.
Spark Plug Baseline
Use the spark plug as a quick diagnostic baseline: heavy fuel smell, oil fouling, or a damaged electrode can point to the next check.
Confirm the plug gap before chasing fuel-system parts.