We took a mild big block car to the track with a new rebuilt 850 holley worked great except for the first hit of the throttle. At the first hit we have a dead spot after that everything worked fine. The only way to not have the dead spot is to get up on the converter to about 3500 rpm. With another carb off of a stroked small block we have the same problem. Carb problem or not??

Accel pump squirts as you touch the throttle? Vac adv w manifold vacuum?

850 DP? could be a pump shot problem, jetting problem, or timing problem. Usually that means you are lean and need to go up a few jets or your squirters are too big and you need to drop down. I'd try and set the total timing at 38* @ 2400 rpm and go from there...and disco the vac advance. I ran a 750 DP in a mild 440 to 12.90's (67 coronet) w/ 31 squirters 6.5 PV, 78 front 84 rear jets.

The timing is at 38 the car is a 69 roadrunner it ran 6:88 @ 100 the jets are 82 front 84 back squiters are 31 front 28 back