That left cylinder seems to be a common "bugger". As far as the points go, I agree with Ballard- once set properly, they're rarely problematic even though I have since switched to Boyer myself. Prior, though- I didn't really NEED to- just did it as an elective - no regrets. That carboned up plug, however could indicate several things. Is it oil? From where? Valve guides? Valve seats? Piston rings? Maybe try a compression test between cylinders and compare. Maybe a "valve job" is needed. I had a cracked piston ring & didn't know it! I doubt your problem is ignition or carbs if properly set up. But who knows what these things have been through? I bet you're NOT the original owner.
