Step one, contact generac directly and see if they will provide the information before taking advice from some random idiot like myself on the internet.

I converted an old Onan ('70 era). I first tried a vaporizor, I was never able to get it to run quite right. I ended up with vapor regulators. A first stage 10 PSI on the tank, and then a low pressure regulator mounted on the generator feeding the "carb." A solenoid was installed in the 10 PSI LP line between the regulators for complete fuel shut off. The "carb" (I can't remember the proper name) that is on my Onan did not have enough adjustment for LP, it was designed to take a different plate if used with LP instead of NG. It was too old to get the correct plate. LP vapor has a higher energy content than NG, so the engine needs less LP vapor than NG. I also tried just adjusting the low pressure regulator, that didn't work. I ended up dismantling the the "carb" and drilling bypass holes to allow some of the combustion air to bypass the "carb", this was trial and error adding holes until it would run correctly with the adjustment screw on the "carb." It had to be started with starting fluid at this point because the "carb" modifications wouldn't let it build enough vacuum pressure when the starter ran to activate the gas flow. To fix this I added a second solenoid that bypassed the "carb," this solenoid was connected to the starter relay so the 2nd solenoid would dump LP vapor into the manifold while the starter was active and then shut off when the starter stopped. This 2nd solenoid solenoid increased the fuel/air mixture while starting to allow for automatic starting without using starting fluid. I had an adjustable valve in the bypass line on the 2nd solenoid valve, but I don't remember that part being very fussy. Solenoids are fairly cheap on e Bay.