Few comments.
If your search the internet you should find a repair manual for your Onan - that should give you info on your request. Nice to have in the RV at any rate.
Your symptoms are pretty std for gummed up carb - most people resolve that by using Seafoam ... lots of threads on that subject if you use the forum search feature and use the term Seafoam. In general you disconnect the existing fuel line to the carb -- connect a temp fuel line (rubber found at any auto parts house) which leads to can of Seafoam. Start up the generator - let it run for a short while - let it set for a long time ..and repeat as necessary. Your goal is to get Seafoam inside the carb and let it set and do it's work.
Lastly - most small engine lawnmower shops can tune an Onan Generator - worth a thought.
