All OE AVS's are lean from the discombobulated emission requirements of that era (68-71) when Ma & the rest of em were trying to keep up with the strict federally mandated emission stds. convert the tall pri jets/3 step rods to eddy performer short pri jets/2 step rods. a few thou richer on cruise/power might be a good start. AVS strip kits are as rare as can be. EDIT An AFB is a far better carb to work with (if you have a choice).
To the op, thanks for posting this thread. I like Rapid Robert's tip & it may be the solution to my bro's 517 Hemi's lean backfire problem. He's got 2 650 Eddy Thunders (AVS) & after a few yrs, its developed a carb backfire on WOT from crusing speed. Their accelerator pump linkage is already on the top hole & springs, jets & rods were replaced on install. SO maybe, if we can find a qualified tech in Vegas (no old school gurus here), maybe this is the fix. May send them off to Competition Carbs (Oliver), to have this done. Thanks again.