[Jack Gifford]

Not a Pontiac question. I saw a picture of a Mopar 6-pack that had what appeared to be vacuum diaphragms on the end carbs. Were they to open the end carbs (like old Pontiac Tri-Powers) or were they for some other function?

[Tom Vaught]

Jack, about 99% of all of the 340 and 440 Mopar 6-pack carbs used vacuum to open the rear and front carbs.

Instead of a vecuum switch on the center carb Holley actually opened the secondary barrels just like they opened the secondary barrels on their normal 780 cfm GM and Ford 4 bbl carbs for many years.

If you go to the Street Section thread called Some Holley Carb Tips and look at post #99, I have a bunch of info on how the carbs were designed and how the vacuum system works. Also this link to a generic article
http://www.rodauthority.com/news/his...reproductions/

Tom V.

[Tom Vaught]

Basically Jack on the Pontiac systems, as you know, you had a vacuum storage can, a thermal vacuum switch, a check valve, a vacuum control switch, and some metal and rubber line connecting it all together to a Vacuum Pod on one of the outboard carbs.

Basically an on off switch with a vacuum bleed position to shut off the end carbs. The storage tank stored vacuum when the engine was at wot so it could still activate the end carbs.

The Holley system worked differently.
It sensed the center carbs airflow and at a given point the "kill bleeds on the end carbs could not bleed vacuum fast enough to keep the end carbs from opening. At that point the end carbs opened exactly like a vacuum operated Holley 4 bbl.

If you got off the gas the end carb throttle shafts were mechanically connected to the center carb which physically forced the end carb throttles shut. No waiting for the vacuum switch on the Rochester system to bleed down the vacuum from the vacuum pod. MUCH SAFER DEAL.

Why do you ask Jack?

Tom V.

[Jack Gifford]

Just curious. Thanks for the info.
So apparently all three Mopar carbs had more than just the main/pump systems of a Pontiac end carb? Besides intermediate circuits, did the end carbs also have idle and power-valve systems?

[Tom Vaught]

Some very special Mopar 6-Pack Carbs (built originally for the Ford 366 NASCAR Engine) had Accelerator Pumps, Idle Circuits, Jets in the end carbs, etc.

But those carbs were for the most part scrapped later (by Ford when disallowed to be used in NASCAR racing).
Edelbrock later bought the rights to sell the 4782 and 4783 list number carbs (with mechanical linkage) on the Mopar Race 440 6 Pack Engines. Low Volume Deal though. But Holley carried the Part Numbers in their catalog for a few years.

So the typical MOPAR 6 pack carbs used metering plates, had fixed idle circuits on the end carbs, and had vacuum opening of the end carbs.

Tom V.