Dummys guide to carburated engines

One problem is, that carbs "vary." Something like a tractor/ outboard/ small engine carb is much different than a U.S. automotive engine carb. I say that last, because the traditional Brit/ other carbs are also different, they work more like a bike carb. "That is," the throttle is a sliding cylinder which pulls a tapered needle out of a jet in order to control fuel ratio as the throttle opens. some of these have a vacuum arrangement.

Even with US carbs, different ones are ............different........Older Ford/ Holley pretty much all used power valves. Carter/ others/ GM Quadrajet and Carter thermoquad used a vaccum piston(s) with a spring, to push a tapered metering rod up out of a jet to control fuel, "the power circuit.' Holley (and others) power valve is a vacuum diaphragm which opens a little poppet valve, allowing more fuel in addition to the main jets.

The nightmare electrically controlled carbs of the late 70's and 80's before EFI.......the designers should be taken out and shot........many times.........over and over.......with pellet guns