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).

Triggerfish, the messed up calibrations were in the OE (68-71) AVS's only. the later AVS thunders would not have that issue. now you can get the OE AVS's to run like a scalded dog if you put some work into em but for the nth degree of performance there are much better carb choices. but on the early AVS's, He may already have em/they may be required for class rules/he might not want to buy new carbs.

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.

Did those carbs always do that? Sounds like no. What changed?

Nothing except it sat for almost 3 weeks before being driven, so maybe its varnish or contaminants causing it. But it didn't backfire today when he drove it. He's got 2 elec fuel pump systems he can select. One's an Aermotive in tank system & the other a Holley Gerotor pump. 1/2" feed & return lines. No chokes on the carbs.