Generac 4000EXL (Extended Life) generator commonly uses the Generac GN-220 (7.8 HP)
If the engine runs but won't take a load, the manual helps you diagnose if the issue is the engine RPMs (which should be around 3600 RPM for 60Hz) or the alternator brushes. How to Safely Download Manual Archives
This model is sensitive to stale fuel; it is recommended to use 89 octane gas and avoid fuel older than 30 days without stabilizer.