This started awhile back, noticed plug wires being burnt in a few spots. replaced them still have the issue.  Pulled carb a BG JR.. I thought I had it tuned right with a blow proof power valve.  With a 57+ distributor.  New plugs, new wires. So now I don't know if I got a broken valve spring or the dist is going to crap.  Used to run well with the original fordomatic dist and coke bottle carb.  Now it seems to be snowballing to not being driven.