An AFB would be a lot of carburetor for an inline six, unless it was an awfully big one! While the total CFM might be OK at full throttle, high RPM, what about low speed and midrange performance? Too much venturi area results in very low venturi velocity and little, if any fuel flow through the high speed system. The result is a bad flat spot right off idle, or even a stall when the throttle is opened. If you can manage to get it up to high RPM, and stay there, it might be possible to jet it rich enough to run right. Forget getting away from a stop sign, though!
A 350 cubic inch V-8 at 6,000 RPM flows 608 CFM, and that's figuring it at 100% volumetric efficiency. Realistic VE is more like 92% on the average street engine, so that brings the effective CFM down to 560!
A 250 engine at 8,000 RPM only flows 578 CFM, so you'd better build that bottom end pretty bulletproof!
Jerry
