Yes, In order for the 2 bbl carb to open the 2nd bbl, the primary throttle in near wide open throttle, then vacuum pulls the secondary throttle open. <P>Yes, This is very strange to me too.... i'm used to mechanical linkage opening the secondary.<P>The Vacuum pulls a diaphram in what mitsubishi calls a "depression Chamber".<P>It is located at the Rear of the carb on the engine side... (yes it is buried) <P>see for details: <A HREF="http://www.outdoorwire.com/content/4x4/mitsubishi/tech/mikuni/" TARGET=_blank>http://www.outdoorwire.com/content/4x4/mitsubishi/tech/mikuni/</A>