Backfire on deceleration

[Bombasstic]

I have just rebuilt my carbs. I replaced everything except the pressed in idle jet and the floats.
My bike runs beautifully but backfires badly on deceleration. I have fitted new Air Cutoff valves and I have done a carb sync.
I believe I have all of the holes and channels clean and open.
Is there anything else other than the Air Cutoffs that can cause the backfiring?
I have noticed that while idling, pulling the plugs leads on #1 or #3 makes a very noticeable drop (almost choke off), but pulling #2 or #4 only causes a very slight drop. This is most likely due to pilot setting which I find very difficult to do ?????? I have got all 4 pilots set at 2 turns out. Could the pilots have anything to do with the backfiring issue ?????
Any help will be appreciated.

[tomos]

Initial setting is three turns out on 82 and 83,and 1.5 on 81.
Most likely there is not enough fuel when you close throttle.
Good luck.