What is the most likely cause for a generator start-up failure?

The most likely cause for a generator start-up failure, especially for portable gasoline generators, is stale fuel and a clogged carburetor due to long-term storage without proper preparation. Gasoline begins to degrade in as little as 30 days, and when left in the carburetor bowl, it evaporates and leaves behind varnish and gum that clogs the pilot jet and main jet, which have extremely small orifices. This prevents fuel from reaching the engine, so the generator will crank but not start. Statistics from small engine repair shops indicate that over 70 percent of no-start complaints after storage are fuel-related. Other likely causes include a dead or weak battery on electric start models, old spark plugs fouled with carbon or oil, low oil level triggering the low-oil shutdown, a clogged air filter, or the fuel valve being left in the off position. Less common but still possible are a stuck float needle, water contamination in fuel from condensation, or ignition coil failure. The best prevention is to run the generator dry before storage, use fuel stabilizer, drain the carburetor bowl, and exercise the generator monthly for 20 minutes under load. If it fails to start, start troubleshooting with fresh fuel and a clean carburetor.