square bore vs spread bore 440

[dodgey68]

G,day dc.com
i currently have a square bore 770 vacuum secondaries carbie on, runs quite ok, but i sortof miss the the square bore secondaries throughty noise and feel when ya floor it, i recently got hold of a Holley (6210) spread bore  manual secondaries,  fitted it went on a tour, had some fun,, but after a little i put the foot down , the car cut out on me, after 5-10 minutes, it started and i was on my way,,i reckon with the secondaries on particular Holley,  open it flooded it , put the fire out so to say,, its a reasonably standard 440 , ,, im guessing the secondaries jets are to big??  any ideas,,,
what is the pros and cons of spread vs square??  your views

[flyinlow]

The idea behind the spread bore is small primaries that maintain a high airspeed thru the venturies during normal driving for good fuel metering. This is the same concept as a square base four barrel ,just taken to the extreme. The Quadrajet and Thermoquad carbs (speadbores) where good for their time, but have been out of production for almost forty years and support is lacking today. I have used TQ's on several cars. On stock or mild engines they run well. The limitation I have found is their limited accelerator pump circuit when used on large volume unheated aftermarket intakes. (both current Chargers)  The TQ is a manual secondary carb ,but has an air valve to slowdown the large secondaries until the engine is ready for the extra air.

Most carb manufacture's recommend VS carbs for B body street cars. I have a Holley 770 street avenger on one and  Quickfuel 780 Hot Rod series on the other (just went to EFI because I can not leave things alone.) on the other. They both do pretty well. The Quickfuel carb is easy to tune . It did not need much tuning , except for the accelerator pump needing more. I have a A/F ratio gauge so you can see what the carb is doing while you drive.

If you have a 4.10:1 axle or lower with a manual or high stall converter where you can get the engine up to 5000 rpm+ where it can use that much air before the accelerator pump shot burns off buy a Holley 750 double pumper.

I did try a friends old Holley 650 spreadbore double pumper on my Charger (mild build 440) and it drove ok. A little less top end power then the TQ I was using at the time.

All carbs sold today except for the Demon carb thermoquad knock offs are square bore carbs.

While jetting could contribute to the issue you talked about, insufficient accelerator pump discharge or secondary opening to soon would be what I would look at first.