I made a flame thrower on a homebuilt chopper. I tee'd off of the fuel rail (50psi) and ran the fuel line to the exhaust about 12" from the exit. I put an in line 12 volt solenoid to control fuel. I tapped into the coil driver ciruit that fires the coil (EFI) ...with one switch (or horn button) i can deliver fuel and ignite the coil. I put a spark plug about 5" after the ex outlet. You NEED fresh air or it wont light . If you can intodue air into the exhaust upstream that would work too. It is safe enough, depends if you scream like a little girl when you take a can of ether and ignite it when seating the bead on a truck tire....