A carb configured like the 850MD, 1.560v x 1.750, downleg booster, DP, can be a challenge to get to leave hard....... even when it’s the right size for the motor combo it’s sitting on.
Which in this case...... it’s def not.
Add in the 8000’ DA and it just gets worse.
Watching the vids of it on the motor, looking down the carb during the attempts at winging the throttle and seeing it’s not anywhere even remotely close to working as well as it would have to, to get good launches by footbraking.......it’s time to accept that no matter how much you mess with it....... it’s not going to work as well as something that’s just a better match for the overall combo.
If you’re having a good time messing around with it, that’s fine.
The fact that there’s .2+ gain in the 60’ by swapping to another carb tells the tale.
On that combo, at that elevation...... it’s the wrong carb.