Glowing Headers

Ok, it was at idle for 15 min. or so, just changed plugs 2 days before. he set timing with a light that has timing degree display on back, its a carter 4 barrel (stock on my 340 i think) it has my 340 manifold on it (could it be laeking - just installed?)yes vacume advance. he was doing something with the vacume lines while timing it. i think it gets vaccume from the front of the carb. and last how would i fix a fuel distribution problem.