Some, mostly smaller AFBs, didn’t use a velocity valve. That’s why Edelbrock sells the 625/650 cfm carb for 350s in general.īy the way, the velocity valve is the counter weighted flapper below the secondary venturi clusters in many AFB carbs. It allows the 625 carb to work on a range of engine sizes. However, on the AFBs there is a velocity valve which limits the secondary air flow so that you can use a slightly larger carb. Maximum air flow for a stock engine like a 290 HP Chevy 350 is less than 500 cfm if the secondary on the carb was a plain venturi type, you would have to use a small carb. Now, if a carburetor provides too much fuel for the amount of air, then it will run too rich, but that’s not caused directly by the carburetor being too big.Īs for the common Carter Competition AFBs (made up to 1984 by Carter and sold up to about 1998 made by Weber) and the current Edelbrock AFB, the primary side is the same size in the Carter 625/Edelbrock 650 as in the 500 cfm version so there wouldn’t be any difference in part throttle driveability between the 500 and 625. So, it is not that too big a carb (too many CFM) will provide too much fuel, rather that it will provide too much air and fuel. In other words, when the engine is operating at high speed at Wide Open Throttle (WOT), how much will the carburetor allow the engine to breathe.
In fact, CFM refers to the maximum Cubic Feet per Minute of air/fuel mixture that a carburetor will flow.
(Carter calls it 625, Edelbrock says 650 – same carb). No, the usual size on a stock engine like that is the 625-650 carburetor. Edelbrock AFB Carburetor - Uses Rebuild Kit CK294 The Answer…
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