I recently did some research on the vacuum secondary pod and noticed some options on tuning with them and some simple modifications that is easy to do and I can post some information later on but you want to figure out your primary side of things first. As stated up the jetting some but also if you have a chance is your cam the roller version or the flat tappet?
I have not had my hands on a holley 770 street avenger in many years so I don't know right off hand on what the air bleed and idle feed restrictor sizes are but I can maybe guess here that its very close to the 3310 750 vacuum secondary carb.
What is your timing curve as that can affect things. I once had a issue like yours and no amount of carb changes would help and I found out that I did not have my distributor set back right after changing out a new rotor and cap on it. I was off on my timing by a small amount that was enough to give me tuning fits.
What color pump cam is currently on your carb and what size shooter? After figuring out your primary side of things I can round up my research and photos and post here or maybe in the 670 street avenger post on the secondary side of things. Also is your street avenger the 2 corner idle or 4 corner idle and of so how far out are your idle mixture screws?
Last edited by eric32; 11-26-2018 at 10:10 AM.