I would say that if you are getting spark than you are not getting fuel. If one side is getting hotter than the other than it might be not so much a carb issue rather than a fuel issue. so check the fuel line at and after the tee junction off of the fuel tank. Since the two cylinders are hotter than the other, it leads me to believe that your tee junction or fuel manifold is gunked up. ( meaning two carbs are fine, the others wont fire and the problem is symmetrical.) That is step one. Or would be if it were my bike. If everything seems to be fine with your fuel line and you are pretty confident that you are getting fuel in to the engine then I would look at your head to see if your valves seal correctly. assuming that your timing is correct.

hope that helped. good luck