A friend of mine in the commercial generator business would say, the problem is that it is a Generac!
Has nothing good to say about them.
How many RPM does the unit run at, just out of curiosity?
I actually installed one (on Propane) at the request of a customer. My feeling, and hearing the thing run at 3600rpm is that it won't last long! Maybe the regular excercise has already worn it out.
you generac naysayers drive me nuts. Ive been installing generators for nearly 30 years. Big commercial units and smaller residental units. Ive installed Honeywell, Generac, Siemens, you name it.
Funny thing is, alot of other manufacturers use Generac manufactured engines and parts. Generac is the WORLDS largest generator manufacturer.
Ive never ,... never... have had a call that a unit failed due to generator manufactured issues. they have always been from misuse or neglect. I just fix two units that wornt working after a power failure. The owner NEVER changed oil or checked batteries since they were installed. They were installed 7 years ago. After servicing them, they both fired right up.
Nothing will last if its not maintained, and most people forget their generators.
Now for the OP's issues. I have run into similar issues in the past. I assume that this is an air cooled unit, so ill not worry about heaters (extreme cold kits). Things to check
1. check that gas/fuel solenoid is opening.
2. Spark plug foul and check gap
3. Fuel pressure set wrong
4. The manual talks about checking #14 wire on the control harness to make sure its connected, but this is quite a chore to do.
5. A week battery will cause a weak spark on the sparkplug. You can do a spark plug test like you do with a car to check spark.
just for your info, ive also fixed a unit where the installer used pipe dope not rated for NG on his generator install, and a large clump of it broke free and obscured gas flow. Found that after unhooking the fuel lines. This made the generator act erratic....rev and stall, hard starts.