SO Jim, you figure the issue is a gummed up carb?
Could be, or a similar issue related to use of ethanol fuels - hard on hoses and gaskets in devices not originally designed for ethanol.
I was thinking more along the lines of a mechanical issue - possibly a carb linkage issue where a change of adjustment, or drop of oil would solve the surge. Not sure what engine RPM control scheme Onan used in this particular generation design, mechanical, or electronic - or a mix of both.
Guess I'll wait for a few more suggestions, and also drag out my Onan manual to get a bit more insight into how it all works...
John Day....|'88 Winnebago Super Chief 27ft. Class A
Eastern .....|'88 KIT model 240 24 ft. 5er
Oregon ......|'02 Dodge/Cummins 2500 Quad Cab