Dollar to a donut it's the accelerator pump circuit. If it is, often this condition will lessen as the engine warms up, to the point where you'd not notice it under normal driving conditions.
Check to see that you're getting a shot (not a dribble or a bubbly/frothy discharge- you should get a mini-squirt gun effect) at the instant you open the throttle.
The fix can be setting the pump linkage to a bigger sho, or a new accelerator pump piston, lightly honing the pump cylinder, or possibly the check ball isn't seating or is missing.
A tip if you choose to try using a different hole on the accelerator pump arm: When removing the accelerator pump arm roll pin, place a ~0.050" feeler gauge (or similar thickness material) behind the accelerator pump lever pin (between the air horn and the roll pin, in other words), so when you drive the pin towards the air horn lip it doesn't butt tightly against it; instead there's room to get a thin straight blade screwdriver in behind it to lever the pin back into position. Using the hole nearest the roll pin gives the biggest pump shot.
But sometimes if the bore is worn, going to another hole regardless if its for a bigger or smaller shot size can help, but if this is the case the better fix is to lightly hone the bore and replace the piston unless it's new.