I've heard several theories about the rubber boot on the Ram Air units, and Pontiac Ram Air carburetors were the only carbs to use that set-up even though cheap over the counter kits come with the wrong pumps and the rubber boots and retaining ring for non-Ram Air units. Well they used to, but those parts are all now discontinued. If anyone has any rubber boots and retainers, contact the shop we are buying them.
One thing it does for sure is reduce wear in the airhorn where the pump shaft travels thru it. Almost all Ram Air carbs that we build are super-tight on the pump at that area, compared to all others which usually have some clearance there from wear.
For sure the boot and retainer seal off that area, maybe the engineers knew something we didn't about having "Ram Air" on those engines and thought it might put a slight amount of pressure in the bowl and they didn't want any seepage around the accl pump shaft? I can assure everyone reading this that Ram Air systems do NOT pressurize the bowl of the carburetor or cause a leak there, been running a real Shaker assembly on my engine for decades with zero issues in that area....Cliff