So I have been finding the Jr to be a lot trickier to hit than its bigger brother. The full size brick I feel like I really have to try to even get a scorched hit, and I have yet to combust at all. With the Jr I keep alternating between barely getting a hit, or scorching the load. I took it to a friend's place (friend who is open to vaporizers but is still primarily a smoker) and he combusted on his 2nd try (partially my fault, as his first hit was barely a hit at all and I encouraged him to get in closer with the flame.)
But I think I may have solved it. As you probably know fire doesn't pass through a fine mesh screen. My thinking is that it is not that there is too much heat causing scorching and combustion, but rather that flame is still present and makes it to the load, especially with the shorter air path. So I stuffed a screen up into the metal ring under the intake. I still need to do some more testing to be totally sure, but I am pretty confident that this will reduce the chance of combustion by quite a bit.
My initial test after putting the screen in was to use the torch I use for the full size brick, which is turned up quite a bit higher than the torch I've used with the Jr. Got a solid hit (from an already mostly cashed bowl as I was really pushing it and still expected to combust) and a nice toasted color in the load but no scorching.
I initially thought of putting a smaller screen directly under the glass tube, but didn't have any the right size. But I have a bunch of screens roughly the same size as the ones for the Brick's bowl, and once I worked it up in the metal tube it seems pretty snug and probably won't slip out.
I noticed a couple pages back (and similar discussion just a couple posts ago) about putting screens before the bowl to prevent the load from spilling out through the intake tube in transit (or to use the Jr upside down) and you guys may have inadvertently solved two issues at once.
After I have had a chance to put this setup through some more paces I will follow up. (I would have given it a good solid testing already, but yesterday was super busy with a dinner party at a friends house and then I had won tickets to see legendary reggae dub madman Lee "Scratch" Perry last night. He turned 80 this year!)