backfires when i turn key off

I always like to go back to what was recently touched/modified, so i'd want to double check the wiring, especially the coil, and distributor. The Street master is a single plane iirc. Hard to figure why one side plugs would be wet. I could see front half (primary) or rear half (secondary) if a float was stuck/sunk.

Don't chop my head of guys, but i have to ask.......How old/miles is on the timing chain?