Air leaks

The rear cylinder on my 77 IH isnt firing. I was gonna ride my bike today and went out to start it and it was a pain in the ass to start. when it finally started it didn't sound right. It had been missing from the rear cylinder. I put my hand over the exhaust pipes the front exhaust was hot and the rear was cold. The bike will only run with the enricher all the way up. I talked to George at work today and he said his bike was doing the same stuff, and it turned out to be an air leak. I know the common place is at the intake manifold so i took it off and checked the seals, they looked ok I made sure the clamps and seals where tight against the manifold and reinstalled the carb (S&S E) and the same thing happened , rear cylinder not firing. I checked the plugs, they where fouled. I tried to clean them up and checked the spark and it was good. The rear cylinder was still not firing. Now I can hear the leak but I can not fully determine where it is leaking from. My question is where are the places taht these are likely to develop or what are possible alternate issues I could be having?

[Pa]

Try a little soapy water around the spark plug. Try a pair of new plugs also. Pa

In case anyone cared the cylinders where scored, BAD, so I did a .020 over bore and rings pistons and gaskets and soon,I hope, it will roar (to my delight not the neighbors) to life.