I have a Holley 670 in my 86 T/A. Its a 3970010 350 block with 624 heads. so far it has a Holley Street Dominator intake the 670 carb and a 2.5 in cat back. Now my problem is when I stomp on her the motor shudders and then tachs up. Is this a problem with my A/F ratio?

Probably a problem with the opening rate of the secondaries. You probably need a stiffer spring.

If you're willing to spend $40, I'd recommend the Quick Fuel Technologies adjustable vacuum secondary housing, p/n 63-1. You adjust opening rate with it via a needle valve in the vacuum signal circuit. IMO, that's the only right way to control the secondary opening rate with a vacuum secondary carb.

I think its mechanical 2nds...Is this just a common carb thing?

You said it's a Holley Street Avenger, and 670 CFM. The only 670 CFM carb Holley makes is a Street Avenger, and all Street Avengers have vacuum secondaires - although they are 4150 style, unlike the typical universal VS Holley.

It's a pretty common tuning thing. Make sure you don't have a vacuum leak somewhere.

If it was a jetting problem, it wouldn't recover. Although, richer jets in the secondary may help it a little, but it isn't the proper way to "fix" it.