When you said how much to open my idle mixture, it should be the other way around. When it is knocking, that is because it is loading up with fuel. Had the same problem with my magnum, but they are the same exact concept for adjusting them, it just may be a little different. I had to close mine 1 1/2 turn from factory setting, now when I move the throttle to idle cutoff, it doesn't want to quit! For what your experiencing, turn it in 1/2 turn and see if that help. Get it good at 3000 before you try going lower, because the slower your engine is running the more it will load up with fuel. If you can run the engine so you can look at the idle needle you will be great, because you can run it and just close it in until you hear/see it running better. About the carbs being defective, if you get your idle mixture all the way in and it's still running, I'd say take it somewhere and see what they say. Good luck and let us know how it turns out.