AKA "air vent cut off diaphragm"
This little guy keeps a valve closed when vacuum is supplied or held to it (engine running). When the engine is shut off the valve opens and fuel vapors are directed into a charcoal canister, rather than vented into the atmosphere.

When the diaphragm is perforated like mine is, and engine vacuum declines (when you hit the go pedal) the valve opens and creates a huge air leak. So no go with the go pedal.

I found the description of how this system operates (when working properly) in the emissions section of my service manual

and figured it out from there.

Unfortunately I cannot find a new diaphragm. Honda has discontinued this part, it's not in the rebuild kit for the carb, and I can't find it in the aftermarket anywhere.

So my choices are to either paste up the rubber with some sort of bonding agent and hope it works, or eliminate this part of the emissions system (all emissions systems must be in place and APPEAR to work)

So for now I'm using a less perforated diaphragm scrounged from another carb and MrHanky drives a whole lot better.