Thermoquad to lean ?

hi there, hopefully someone can help me with my TQ issue
but first some specs.

engine: 273cui 040 over, low comp pistons
cam: (similar to an 340 stock cam),
heads: 318 stock heads - ported, bowl blended
headers: Long tube

intake: orig. 340 mopar TQ intake from the 70ies
ignition: rev-n-nator box - 18 ° in idle (Distributor with an 18 degree stop plate - so max will be 36°)

trans: 904 with shiftkit
converter: stock
rear end: 3,91 sure grip (26 Inch tires)

carb: TQ 850 cfm

Problem: on low speed like City traffic, e.g. when leaving a Rotary and trying to accelerate i will get backfire sometimes.

when hitting the pedal right from an stop - i will have something like a bogging or a dead point and after a few milliseconds it will come back and roar and pulling like hell.

i tried to adjust the airdoor - which cures the symptoms a bit but i´m a bit worry to go to far and end up with messing up the spring) it´s now 1 and 3/4 turns from that point when the air door makes contact when giving tension to the spring

i also tried to adjust the idle mixture screws. max vaccuum is reached with 4 3/4 turns, but then it still has this backfire. the backfire is now gone with 5,5 turns.

the accelerator pump is set the way, that it will spit when the throttle lever starts to move (within the first 1 or 2 Millimeter)
but in my opinion it is only a minor squirt compared to what my former Holleys or Demons have made - would it be an option to open up the squirter nozzles a bit with a drill to achieve more squirt ?

maybe the carb is to lean in General ? to be honest i do not know what size the jets in the mainbody are

any hint will be appreciated (as i want to go to the track next Friday/Saturday)
thanks