TOPIC:

Does anyone know what the slides with the rubber diaphrams actually DO in a CV carb? Is a perfect seal on the top end of the carb important in CV carbs?

Inquireing minds want to know

Is a perfect seal necessary? Um? Yep it sure is!

In order to keep the air velocity from dropping too low on rapid throttle opening. The action of the carb slides are actually controlled by the amount of vacuum available in the intake tract. That way you can't wack open the throttles and have the vacuum drop to nothing before the engine can pick up speed.
Bill

The rubber slides actuate when engine vacuum is increased; as when you open the throttle. Since the slides raise when actuated, they control the position of the jet needle with respect to the needle jet; the more raised, the more gas, due to the taper of the jet needle. Once fully raised, the main jet is metering gas.

If a slide is holed, torn, damaged, etc, that slide will not raise as it should and performance will be adversely affected.