Thanks for everyone’s help and advice. As it turned out the problem
was quite simple and probably stupid. I used the wire “stand” that
came with the kit to hold the tanks steady. However, it tilted the
bottles. After I bought new tanks I did not put them in the stand
and kept them upright and had no problem lighting the torch. I tried
the old ones again and they worked too. How is the wire stand
supposed to work? and of course, now I am a bit confused whether to
turn off the fuel or oxygen first. GOOG sounds most reasonable. Does
anyone know about flashback arrestors for disposable tanks? Uli