Hello everyone, new member here and I did do my best to search the forum for my symptoms, but I haven't found anyone posting anything similar. I just picked up a basket case 78 XS400E and went through it all and got it running (cleaned and regapped points, set initial timing, cleaned and reset carbs, etc). Now however, I seem to have an odd symptom, that I think only showed up now that I've "blown the cobwebs out". When ticking over there is an air leak hiss sound from the right cylinder AND if you put your fingers between the head and the spark plug, you can feel puffs of air. Looking in that area behind the plug, it is finned and hollowed out for cooling purposes, but I don't see any soot or black exhaust residue. Compression is 115 for left side and 100 for right, so low, but not terrible. That cylinder does fire, and once warmed, seems to be fine.
So my questing is has anyone seen a 400 head crack from combustion side to that cooling hollow? Could it just be a crack in the exhaust port through to that area? Though I doubt this as you can feel the puffs of air with decent force and I'd imagine that exhaust port and open muffler would release that pressure pretty quickly. I guess the next step would be to pull the head and check it out?
So my questing is has anyone seen a 400 head crack from combustion side to that cooling hollow? Could it just be a crack in the exhaust port through to that area? Though I doubt this as you can feel the puffs of air with decent force and I'd imagine that exhaust port and open muffler would release that pressure pretty quickly. I guess the next step would be to pull the head and check it out?