Thermoquad mods that work.

Rumble.
Yeah the differences in the air door [AD ] of the Comp Series & production carbs was what I was referring to. The shape of both carbs in that area look similar, so why the change, I do not know.
Only thing I can think of: as the AD starts to open, more air gets past the AD on the CS series on the initial opening; secondaries activate sooner?

I have a couple of CS 850 carbs. After doing the above mods to a production carb, butt-meter could not tell the difference between the two models.