Here's a suggestion to help you save time from continuously searching for the blockage in your accel pump. give up the air, and use carb cleaner for this.
you'll need to work backwards through the system. once you check one item, and it works, move on to the next. pretty soon you will find the part or area that needs attention.
you'll need to have these carbs off the bike but all together, the accel pump fuel lines OFF, carb bowls off and accel pump disassembled.
#1. start with the nozzle system. take your trusty can of carb cleaner, and spray into the male fuel line barbs of all the carbs to see if the nozzles spray. DO NOT PASS GO until all 4 nozzles spray and the male barbs on carbs 2&3 spray straight through.
#2 spray UP into carb #2 at the point where the #2 carb bowl check valve meets the carb body. its a really small hole. if you get spray, out of the nozzle, and its male fuel line barbs, move on....
#3 Carb bowl #2 check valve. spray up into the bottom of the carb bowl, where the accel pump mates to it, and see that you get spray out the check valve. if you do, move on
#4 put the #2 bowl back on the carb rack with the 3 screws. dont forget the o-ring at the check valve. tighten the screws as you normally would. spray carb cleaner up into the bottom of the #2 bowl as you did in step #3. do you get spray out of the nozzle and male fuel line barbs. is your o-ring to fat and causing the check valve to be blocked?
#5 spray carb cleaner into the accel pump bowl check valve. does it spray adequately. it should come out fast and in a spray. if it does, reassemble the accel pump onto the bowl. and insert all of the cleaned and clear connecting fuel lines, including the brass spacers between the carbs.
connect an auxiliary fuel supply to your carbs so that all the bowls fill.
i'll even use a really short stiff section of fuel line and attach a small kitchen funnel, and fill the bowls. the short fuel line should be able to support the funnel without your help. fuel will start build up in the funnel when they are all full. stop adding gas at this point. dump some out if you need to. you only need enough to keep the #2 bowl filled.
#6 actuate your accel pump rod to prime the system. either turn the throttle bell manually(i hate fighting the return spring) or get a small screwdriver onto the tip of the pump rod. press it up and down. you should have spray after the system primes. if you dont, you need to recheck your diaphragm and spring setup....its the last link in the system, and you verified all other parts were working.
hope this helps....
