check the air vent lines in 3 & 4, if they are restricted then fuel won't flow because the air won't leave.

and synching them won't do much fopr that problem, but don't worry the carbs until you check the valves, once yo udo that, you do not have to go back and redo things, does no good to synch carbs if you haven't done the other stuff first.

need a cold engine to lash valves, need a warm engine to synch carbs.
H.C.C.M.F. Local 6978