[sharkbite]

With my new Mighty Demon I need to come up with a different pluming system. I found this one that BG recommends but why would the bypass reg be after the carb instead of before? Wouldn't that defeat the purpose of having a reg? I'm using an electric pump at the stock tank and Mallory 4309 bypass reg. I included a pic of how I used to run it with my street demon and the diagram the BG has on it site.

[GoatDr]

The pressure regulator doesn't know where it's at. It just keeps the pressure at the proper level, either before or after the carb. It's still on the supply side of the pump.

["QUICK-SILVER"]

Lets rephrase your queston to; why would you return fuel to the tank BEFORE filling the carburetor, when keeping the carburetor full is the purpose of the system. It's not for making sure there's adequate return to the tank.
The supply line is what you want regulated, all the way to the carburetor. Then any left over can go back to the tank.
The regulator can't control pressure once it leaves it. The needle and seats hold back the pressure. That's why people see unexplained fluctutions at the carburetor and think they need more pump.
Dead head has to be before the carburetor. On return style, after makes perfect sense to me.
Not saying what you had wont work. People have been doing it that way for a long time. It's just after with return will maintain constant pressure at the carburetor without pressure fluctuations.
Plumbed likes in the diagram, several here wouldn't be having to go to extemes to maintain constant pressure at the carburetor.
Just look at modern fuel injection and it might make more sense. Steady pressure at the carb is what you're after, not steady pressure to the return.

[Tech @ BG]

Basically it sets up a "loop" pressure and lets the fuel pump run cooler for extended use. The only draw back to this type of system is in a drag car if it has a real low 60 foot time you could stall the fuel in the line when the car hooks and leaves but for decent performance type street cars we have been using that set up for years now. With the diaphragm bypass that close to the carburetor it also helps with the response time as the needle and seats open and close.