I don't remember if you mentioned which carb you have. But when I was running a Carter AFB, I also had to increase the float inlet needle orifice size about 3 higher to allow gas back in fast enough that the motor wouldn't drain the bowls down. If you have an in car fuel pressure guage, check it at the end of track as you go through the lights, if it is as high as when its idling, your fuel pump delivery should be adequate and your issue may be elsewhere. Good luck.
If you're ever at Firebird look me up, I have the primer grey Demon.
Chuck.
