Miller Carburetor

[midgetracer]

The carb I have has the vacuum piston with an adjustment on the spring. I assume that by putting less tension on the spring, I will lean up the mixture. Does that make sense? I also have a mixture screw that does not seem to do anything. I also have a idle stop screw that sets the idle stop on the rotary venturi. Any help is appreciated. I am trying to locate a copy of Mark Dee's book to borrow. I have found one for sale on Amazon, but it is very pricey.