I was using one of these propane torches yesterday to torture some
weeds and grass that had sprung up between some paving stones.
I have used this same torch for sweating copper and never had any
problems, but it was never on for as long as it was yesterday.
What I found was that after a few minutes (4 - 5?) of torturing weeds,
the flame would get sloppier and sloppier - I'd lose the blue core,
the cone shape would deteriorate and eventually the flame would just
be a messy cloud of flame with no defined shape.
The other thing that would happen is that when I would turn the torch
off, the gas seemed to take forever to shut down and a small (1"?)
flame would hang around the tip for a while.
If I let the torch sit for 10 minutes or so, I could get another 4 - 5
minutes of burn time before the flame went all screwy again.
At first I thought it was the canister, but I tried another one and it
did the same thing.
Do these things have a duty-cycle that I wasn't aware of? It was
almost like the valve itself was screwing up since the torch seemed to
stay on even after I shut it off.
Could it have been freezing up?