timing issue or electrical?

challenger_moe said
its not the accelerator pump it works fine. need to check timing and see if there is a vac leak

Define working. Just because it moves, does not mean it's functioning properly. Did you check for pump shot?

You need to see an instant shot of gas when opening the throttle. If you do not see that, that is what is causing the flat spot.

The problem in your vid without a doubt sounds like you have a flat spot when you hit the gas.

By the way, what carb are we looking at here?