I used the wonderful Carburetor rebuild guide written by Ed Ness to completely rebuild the 4 carbs.
The engine starts immediately (hot and cold) and runs fine except the fact that cylinder #2 exhaust is cold.
Things I verified :
1. Spark for cylinder # 2 outside the cylinder looks good. Switching the plug + cap with cylinder #3 didn't help. Problem remained at #2.
2. Compression at cylinder #2 is high (~ 150 psi) and during vacuum calibration I noticed good vacuum coming from cylinder #2.
Also the engine sounds smooth with no mechanical noises whatsoever.
3. I took off the pilot screw from carb #2 and sprayed carb cleaning liquid in its hole in order to bypass the carb and indeed cylinder #2 started working.
4. I drained the screw at the bottom of the bowl at carb #2 and verified that there is a splash of fuel coming down.
I also performed float level calibration as Ed Ness explains in his guide.
5. I took apart the carbs again and verified that carb #2 has all jets clean and open and that all passages are clean.
I'm confused... Mechanically and electrically all is good with cylinder #2 and it seems that carb #2 is not providing fuel but I cannot find anything wrong with it ...