Hey guys, i bought a 76 monte carlo a few years ago from an older gentleman, he bought it new back in the day still had the bill of sale and all. I like to try and do the work on my car myself, i'm newer to old school engine work however I do lots of research before diving into projects I know nothing about. Not clueless but not as experienced as a lot of you guys out there.

Anyway, Cylinder #7 on it is causing a real nasty misfire all of the sudden. I have always had problems with it building up some carbon on the spark plug for whatever reason causing it to foul up much faster then usual. Normally i just swap it out and it runs great again, at first I thought it was oil causing this from a leaky valve cover, but after swapping valve covers it still persisted. This last time i just swapped the plug out it still has a nasty miss on acceleration, i swapped all plugs and wires, made sure gap was correct and quad checked the firing order. If I unplug Cylinder #7 it runs "great" and there is no nasty miss however upon putting the wire back on #7 the nasty miss is back and loss of power on acceleration. By "nasty" miss I just mean it sounds like really really bad, that probably doesn't make sense.
I'm going to do a compression test this week to verify its either no or low compression, I've attached a picture of how the spark plug came out. (Yep it came out like that.)

Basically wondering what some more experienced people would look at first as problems at this point. I'll check back in with compression results.

 

Valve seal would be my guess

 

Valve seal would be my guess