So our Onan was doing the same thing. I pulled and cleaned it and fought it for two years. Finally I purchased a carb off Ebay and replaced the factory unit. Started immediately and has worked ever since. I changed to only adding non-ethanol fuel to the generator tank and my fuel station tank. Same thing with my sons Can-Am DS90X and it has worked perfect ever since. The generator carb was replaced two years ago and will start and run great every time I try it now.
That was my route and it worked. I know others have had luck cleaning and replacing parts but this was fast and worked perfect.