Having used a MILITARY flamethrower-the M9A1-7, a couple of thoughts.
With LIQUID fuel, a huge amount is burned on the way TO the target. This is overcome by 2 means- First, use of a thickened fuel (think jelly) which increases the range. Second, use of a "wet shot". Put fuel on target. THEN light the igniter on the gun group, and light the fuel.
The other thing you really want to consider if you have not taken your asbestos pills today- like a fire hose, a real flamer shoots a large diameter stream at very high pressures. Understand recoil? Now, lets hold the gun group (nozzle) to one side so that recoil is not straight back, but tends to spin you in a circle.
If you have a lit flamethrower, and spin in a circle, this does NOT endear you to your friends and co-workers that are near to you.