from the q,a on bg link[Open Reply - John
The Barry Grant Demon inline blower carbs number 91012062 for 525cfm, 91012064 for 625cfm, and 91012066 for 725 cfm carburetors are designed strictly for blower or supercharger applications where boost is provided. The power valves and internal components are changed and become load sensitive for smooth operation. The vacuum secondaries are desired for street use and obtain the vacuum at the base of the carburetor. A blown or supercharged engine does not develop vacuum at the intake as a normally aspirated engine and therefore must draw port vacuum at the base of the carburetor.]I think you are just connected to the vac for the sec diaphram[why it sucks fuel,oil]The boos ref pv is at another port or metering plate.