Baja Warrior 200cc Engine Idle Stall

I have a 200cc Baja Warrior... I installed the older style ARC filter adapter and a 3/4 inch RLV muffled exhaust pipe (we run them on the race karts). I am having a problem with this engine, the carb on it is a RuXing carb, but not like the older style on the greyhound motors, it is a newer casting and as a few small changes it seems.. one of the problems I am having is the engine at idle, does not like for you to go WOT from idle. The motor will stall/hesitate for a second, and it will either then pickup and go or it will die. I have tried drilling the low speed up to a 19 and have tried main jets from 35 to 39. This is the first time i have ever noticed this problem on this clone engines, with our race kart motors, I have never had this problem, and the only different seems to be the carb casting looks a little bit different, maybe the low speed or air/fuel mixture circuits are different, I also noticed that the little needle that is on the head side of the bore pass the throttle butterfly on the older carbs is not present on this newer looking style. Like instead of a needle being there, it is almost like the little whole is just drilled for the size and that's it. There is no adjustment screw of course, it is epoxied over with a freeze plug. I also tried another carb and it did the same thing, another RuXing carb, so I was going to try one of the older style carbs off one of my racing motors, but as anyone seems to notice this problem??? Is the idle jet still too small??? It seems to help if I idle the bike up, but it's still there... I didn't notice this problem with the stock airbox, but it may have been doing it very faintly then..

I think because of the EPA, these carbs are coming preset and with the added airflow, it's just leaning them out, and it would send to me drilling the low speed out more would help, but I didn't want to go any further hoping someone may know.

Anyway, I'm tempted to pull the stock motor off and stick at BSP on here with a few hopups, but I may keep it stock too, i haven't decide yet.