Jim,
Well, here's one for ya. The newer 25cc has number 24 stamped inside, and sure enough, your right, the opening is small, but the butterfly is bigger. And also, there is no idle mixture screw and the throttle has detents for three positions, just like the choke butterfly.

The older 30cc has number 20 stamped inside and has a smooth throttle movement like the older 25cc ones I have.

What do these guys do, change the design every week just for the fun of it?

Jim