yeh im with john on that one. Id think thats a ton of carb for that 50cc athena
Performance board smartass disclaimer: Im not saying it cannot be done im saying it might be easier done with a smaller phbh or another carb. 16mm mikuni sounds nice.
With the phbh you gotta get one thing right, then work down from there. The pilot is always open so it affects everything, Start with a good main that is close or too big, then work down. 30 or 32 pilot SOUNDS about right, but the face that you not getting any movement off the stand screams lean mixture. Try raising the needle maybe?
I dont know anything about the opening of the reeds that jon is talking about but it sure makes sense to me. It could be that the 19mm just brings in so much volume of air that this get to be an issuse. Im sure you could work around it. tho.