broke off tap--help

If this is just the air injection hole, I'd say make sure it's dirt/grease free (hose it with brake clean of something) and then just JB Weld it up. The "wreckage" in the hole will plug it most of the way, the Weld will just eliminate any gasses that squeek by. I've tapped a bunch of them... Go slow, and I usually try to run a drill bit through the carbon first, then use the tap but don't threar the whole thing, and I buy these little allen headed grub screws for them. Run the screws up until they hit the partial threads and snug them, and they'll be fine forever.