My father-in-law installed a custom device on one of his Boss Hoss bikes that features a spark plug mounted in the end of each tail pipe, connected to a gas feed directly into the tank. He has a switch that he can flip, which sends gas to the plugs and they ignite the gas. They produce a flame thrower effect a few feet out from the end of the bike and maybe 2-3 feet tall. It's hilarious. It's obviously something that you don't want to do on a municipal road - just on private property. Also, the fireball produces a lot of heat so you can only do it for a few seconds.