If you put the time in to learn how they work and how to modify them they run just as well as a Holley of comparable size.
I think that I spent more money on tuning parts for my carbs than what the carbs cost. I must have over $1,000 in jets, rods, power valves, screw in restrictions, air bleeds, step-up springs, discharge nozzles, vacuum secondary springs, accelerator pumps and pump cams, pin drills, and other specialized carb tools.
I have 2-3 Carter strip kits (because I'm running 3 AFBs currently) and a pin drill set, pretty much all you need to make them go. A touch of epoxy here, an adjustment there and you are off and running.
Oh- The secondaries are adjustable on the AFB, you just need to know how to do it and there is more than one way.
If I have a complaint about the AFB series of carbs it is the fact the newer fuels do boil out quicker when the car is parked due to the aluminum construction. Since I run electric fuel pumps (for one reason or another) its really a non-issue for me.
When I take the 5.9 magnum Duster back out in the spring I'm going to give a Holley (780 vacuum sec) I have here a shot to see if the car turns different numbers. When things are less hectic in a few weeks I'll make a posting inquiring about how the carb should be setup for the application.
Since it is comparable in size (Current carb is an older Carter 750 cfm AFB) it should be an apples to apples comparison aside from the fact one has mechanical secondaries and the other has vacuum.
