I would think that there might be three possible problems, other than vacuum leaks.:
Not enough air
not enough fuel
timing off spec.
The air problem could be fixed by tightening up the throttle cable adjustment. This is not really a proper fix but it might lead you in the right direction
Not enough fuel might mean a needed larger idle jet. I know you went up in size but you might need to go further. Also, have you checked the float level in the carb? If the fuel level is too low it will effect the idle.
Have you checked the timing?