Convert generator to nat. gas question

I bought a 5000 watt Coleman Powermate PM0525312 generator with a Tecumseh HM80-100 engine on it from Sam's Club. I would like to convert the engine to be able to run on gasoline or natural gas. There is an outfit on the web called US Carburetion Co. I sent them an email for information on their product to do this, but they never answered back. Do any of you out there know of a company's that sell these kind of kits to do this? Have any of you ever converted your generators? What's your opinion of doing this to my model of generator? Thanks for your help.