It's ever so slightly on the rich side at idle, and the profile of the KKs makes me think that weak at high rpm is unlikely, particularly the fire... I've had lean backfires before and it's a different sound, more a pop than a sharp crack like this is (and the Kmidget also, when it has it's 'choke' on)
currently set at 4 degrees BTDC. Guess a full re-check of everything is in order, more tinkering (yay!) It's not running the ignition amp yet, as I thought adding more unknowns into the mix without it running flawlessly first was potentially not clever.
it's running one of those standard silver intermotor coils, a ballasted one.
I'll check the coil feeds, the misfire is evident on the rev counter as a little 'blip', if it's bad enough to make fire there's quite a waver on the needle. A little light is a good idea though!
does sound exactly like it's giving up one of the 8 sparks at higher rpm, then burning that5 cylinder's fuel when it gets to the end of the pipe. It's only running the front silencer (the rear one was comically restrictive) so a lot easier for that lot to get out.
Cheers guys, some things to try, helpful as always