In a carb test run by Dunnuck a couple of years ago, the 670 Street Avenger was the farthest off and the most difficult to tune of the carbs they tested. The best was the Holley Street Demon. Nearly perfect out of the box, IIRC. For some reason the 670 is the red headed stepchild of the Street Avenger series. My 570 was up 2mpg over the Holley 1850 that had been jetted down for altitude. It was a really good carb.

The Street Demon with the space age plastic bowl is reminiscent of a Thermoquad, and is probably the latest design you can find. It will bolt on your square bore intake with no adapter. They don't cost too much, either.

R.