Everything looks ok. I think your problem is the curb idle speed is too high. Try setting it down to 750 rpm while in park and if that doesn't solve your problem I would check the timing and make sure it's not too far advanced . Also might want to bring the fast idle up a bit. Mine tops out at about 2500 rpm about 15 seconds after a cold start then when I tap the accelerator it drops to 1500 rpm. When its warm the curb idle is 750 rpm. I don't think the Webers like the really cold weather. On really cold days, without some warm air passing through the venturi, moisture in the air freezes and you get a bit of frost build up on it until the throttle body warms up.