I've been playing with one of these carbs off and on between sessions of removing silver spray paint inside and out (eBay action) and have a few thoughts/questions on the secondary air valve.

It appears that air movement/suction/pressure drop, whatever you want to call it, is the force that opens the valve.

Question 1:
Are these things either 100% open or 100% closed during operation (not counting the time it takes for the valve to move)?

Question 2:
It seems like it would be because of the rocker arrangement - with the carb just about level the air valve almost balances in the open position, but leaning the carb back slightly causes it to close. Is the suction enough to keep it open when the car is going up hill?

Question 3:
Is it possible to reduce the total cfm of the carb by physically limiting how far the valve can open, thereby effectively making it a smaller carb? I was thinkng of rigging some sort of stop on the rocking parts of the air valve assembly in order to do this, but don't know if the suction would be strong enough to overpower the weights and work or if it would just remain closed all the time.

If you get the HP (I think) book on Carter carbs it will help a lot. It has some info on the afb and modifying the air valve. The only mod I remember right off is grinding the weights off to speed up its opening rate. You better find a sorce for replacement air valves when you try this one. One thing I can tell you is that high flow needle and seats are a must for drag racing, my 6000 rpm 327 would suck a 625 dry.

Thanks Marty. I'm looking for a way to make it act like a smaller carb.

Dave Emanuel mentions adding weight to the secondary air valve to slow the opening rate if you've removed too much weight. I'm sure it would work to slow down the opening rate as well.

The book is packed in a box somewhere, or I'd quote it for you.

I ran the same 625 on two 350's, 307 and a bone stock 283. I had the jet,rod and spring kit and was able to tune it for all the street engines and never saw a problem with the av rate.

Chad, I'll get a copy of Emanuel's book. I've seen it for sale often enough - the local library doesn't have it.

Marty, I don't think I'll need the high flow needles/seats. If it works, it'll be going on an engine with about 207 CID, which is why I'm thinking of ways to shrink it a little. It's from a 67 340 CID Buick, and I believe it's a 400 cfm model because of the 1 7/16" primary and secondary throttle bores.

An E-brock 500 cfm 1404 is "on the truck" from eBay, so the book will be a good thing for me to have.

Thanks.