Many can be purchased converted with single , dual or try fuel carbs, Ng
,Propane, Gasolene, from Northern tool and Generac. Honda may have a new
unit out. wwwPropane.generators.com sells conversion carbs of all types.
Ng or propane are nice as they run longer and keep the motor cleaner,
the lower end lasts longer the upper end may or may not suffer on lack
of lubrication, but this may have been solved with Unleaded gas
redisigns.

It is smart to have Tri fuel, in a crisis you wont know your supply.