Does #4 have compression? Probably holding your thumb over the spark plug hole will tell you enough as to whether it will fire or not. A compression tester is better.
Next, if you haven’t done it would be a valve adjust on a cold engine. A sticking valve would keep it from firing.
Knock those off the list before pulling the carbs.
Whatever I suggest here should be given ample time for a moderator to delicately correct. I apologize in advance.
77 WING, 1200 engine with 77 heads, cams, gl1100 foot pegs, Magna V65 front end, 764A carbs, [-gone Suzuki M109 monoshock--, replaced with gl1100 shocks] gl 1200 swing arm, gl1500 final drive, wheel and rear brakes Valkyrie seat, Meanstreak tank, Sportster pipes, Power Arc ignition off crank.
77 Wing. black
83 Wing, in pieces
"Continuing education is important even if the subject matter is fairly useless (as in this case)."---Greg Foresi