Only the 87cc heads have the crossover port, the 72cc versions do not.
Looking at Cylinder #4 chamber it seems that the only exhaust soot is coming out of the exhaust valve. I would think that extreme low compression in a cylinder would produce a massive amount of soot because of the poor burn characteristics unless both #2 and #4 cylinders never fired because of bad plug wires or something else preventing spark and therefore combustion.
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Mick Batson
1967 original owner Tyro Blue/black top 4-speed HO GTO with all the original parts stored safely away -- 1965 2+2 survivor AC auto -- 1965 Catalina Safari Wagon in progress.
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