They've had propane fired weed wackers and leaf blowers for a while now. About time for an outboard. Too bad it's not a Honda!
I remember years ago assembling Commer truck engines in Coventry. As they reached the end of the line, each one would be started and run on propane. The occasional engine would have a sticky lifter. If it couldn't be worked free with a mallet, the engine would be pulled off the line, dismantled to remove the lifter, and the guide was then lapped out a bit - took about 20 minutes start to finish.