Briggs made a kerosene/gasoline engine.
A split tank had gasoline in one side and kero in the other.
Engine was warmed up on gasoline then switched over to the kero side of tank.
Upon shutdown the operation was reversed.
HP does suffer about a 30% loss.
Honda used to sell a G series engine that runs on kero, makes 4HP VS the petrol at 5HP. Pretty sure it was started on kero, I bet it was "fun" to start.
On the farm there's 2 old (hit and miss) McDonald crude oil engines. They will run on anything, I don't just mean oil, in the past they've been run on melted sheep fat(smelt horrible, apparently), melted peanut butter ect ect.
I've gotta try running an engine on sump oil now!
