I have noticed in photos of the QD Engines; the top of the diaphragm
cover has been opened up to expose the diaphragm.

What is the reason for this? Is it to improve the response at the higher RPM's?

Thanks,

Scott is on vacation this week. Not sure if he will be checking the forum during this time. Just so you know. I'm sure he'll answer you as soon as he gets back though.

FWIW, I'm pretty sure it serves no purpose. It's merely because they modified a carburetor by removing it's primer bulb.

Read that, its the way they can see what the condition of the membrane is. Biggest dis-advantage was that everybody wants to touch it and you should not.

Back guys ...

Yes those carbs you "mostly" see are those with purge primer circuit plates removed, bypass hole in casting plugged.
Yes it does allow viewing diaphragm condition, but also allows debris or water to pool on top of it ... BOTH BAD

If careful really a non issue either way.

** Trick for those applications where choking is tough, if you gently press down on diaphragm it allows carb to free flow fuel out the jets which can with some practice of technique save you from finger over intake choking.
*If bladder bag equipped an bag is soft with no pressure within it, some slight pressure against bag while gently depressing diaphragm wil get this free flow of fuel out the jets

Generally, most of the carbs where you see a primer bulb type securing plate over metering diaphragm is done for a visual of the diaphragms shape.
* If you practice a bit you can lightly press on diaphragm to open inlet needle of metering circuit while gently touching the IV bag, this will have carb AUTO FLOOD itself. If done just right, will act the same as finger over intake choking.

** Do note: avoid debris, standing water or contact by any object against diaphragm while engine is running !!

Personally, DON'T like the open diaphragm idea and keep stock covers in place.