Could be a vacuum leak. Check EVERYTHING that is connected to the carb or manifold. Pull the hose off the vacuum spark advance mechanism (distributor end) and plug it, see if that makes a difference. Same for vacuum wipers if you have them. On your first post you said "he played with the distributor timing some". I would recheck the point gap (seems to be a trouble spot on these old distributors) then set the timing right back on the mark. Keep looking, you'll find that pesky little gremlin!!
