www.pulse-jets.com

I am building a pulse jet out of plumbers piping: 3/4' air intake ,2" combustion chamber, 1" exhaust, and a spark plug driven by an electronic grill igniter. I'm using a shop vac on reverse as an air supply. When I try to start the pulse jet, it will either backfire (sounds like a gunshot!) or it will start humming. We turn up the gas (using propane) and the buzzing gets loud. As soon as I pull the air away, the jet will stall out. Any thoughts on why it won't come to an idle without forcing air into it?

Thanks!

Are you using a regulator on your propane bottle? As a rule of thumb: if you think you have too much gas, you don't have nearly enough.
What type of fuel injector are you using and how far down the intake is it?
Is your engine build from known plans (i.e., the pipewood/ ugly stick?)

The intake looks too short, and needs to be rounded inside as much as the wall thickness will allow.