Genny won't start a/ trying to turn on while on shore power.

I agree, there will always be something wrong when you have an older motorhome. I had my share of generator problems, mainly hard starting. I rebuilt the carb twice, replaced the fuel pump twice, replaced the circuit board, and replaced the plugs/wires. It always generated good voltage at 60Hz when it ran.
I finally got it right after being persistant. Onan 4.0 version.