What was your problem "performance wise"? I'm running very low 14's and looking at 13's with an Edelbrock #1407.
Hey bud, I found the AFB to be a sluggish carb vs. the TQ, OE or aftermarket versions (Electric choke models, there also smaller in the primary @ 1-3/8. )
While the primary performance was good, fully opened up, the performance was lacking get up and go, no real punch vs. the TQ.
(I do not recommend the small primary TQ for a stock 400 unless absolute mileage concerns are present.)
My abilty to tune the carb is fine. I was able to just about exactly match mileage between the 2 carbs.
Secondary's of the AFB are not so easy to tune since there a weighted door. Most people do not have the abilty or want to add or subtract weight from the secondary side weighted air valve. Or velocity valve I think they called it.
I don't blame anybody for not wanting to do this. Heck, it sucks.
While it is possible to tune the weighted air door. It is also a huge pain in the butt to get it exactly at it's best. The TQ has a spring loaded door that is much easier and quicker to tune. The AVS is also like this.
So, it is in my opinion, if you have a stock 400 B engine and your looking for everyday performance, the TQ carb is a good choice. It will work for the average guy without much issue. The use of AFB/Edelbrock rods is recommended to use after a 3/4 inch 90* bend is put into them for further tuning use since OE rods are either pricey or near impossible to find.
(I know you probably know all of this, I'm just throwing it out there, maybe for a newbie to discover)