Performance question

[66StangGuy]

iv ben having this problem for a while now.. now shure why but recently after checking everything and tuning up my car i gained a lot more power. iv ben adjusting the timing a little but im still not shure what to set it at. iv tried messing with it and finding different spots to try but still not shure where it runs best. anyway my problem is when i press the gas about 3\4 of the way down is pulls hard. but if i press it to the floor and go wot is boggs a little for a second then catches up but dosnt pull as hard at 3\4 pedal? what could be caused by this? timing or carb related. this is a problem iv always had but probably related to timing or carb. timing too high or too low? currently have it around 14 i think but not shure. what should i set the timing at 302 heads 289 block mostly stock bottom end. thanks.