Quote:
Originally Posted by lust4speed
Jon, I've heard several different sizes quoted for the AFB's used on engines like the '65 421. Were they 575 cfm's?
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They were actually 610 CFM!
HOWEVER
Pontiac paid Carter to place a restrictor between the secondaries to reduce the CFM to 575 on WOT. It would have been uncool for the 4-barrel engine to outrun the more expensive tripower; thus the the "tripower insurance policy".
Pictures:
http://www.thecarburetorshop.com/Hotidle3.jpg
The hot idle compensator on the left is unrestricted.
The hot idle compensator in the middle is restricted, and may be replaced with one like the one on the left if hot idle compensation is necessary.
The restriction on the right is just that, a restriction to allow the tripower engines to outrun the 4-barrel engines.
Very easy to make these back into the 610 CFM by removing the restrictor, or replacing the restricted HIC with the non-restricted one.
To the original poster: As mentioned by Kenth, your carb is a 750 CFM, and calibrated for a Chevrolet. I believe that if you could find a friend to just loan you a "test" original Pontiac carb, you would see the difference.
Jon.
__________________
"Good carburetion is fuelish hot air".
"The most expensive carburetor is the wrong one given to you by your neighbor".
If you truly believe that "one size fits all" try walking a mile in your spouse's shoes!
Owner of The Carburetor Shop, LLC (of Missouri).
Current caretaker of the remains of Stromberg Caburetor, and custodian of the existing Carter and Kingston carburetor drawings.