Two carbs on an inline six with three intake ports is either one too many, or one not enough. The firing order of 1-5-3-6-2-4 means that the volume of only one cylinder at a time is being drawn through each port, three impulses for each turn of the crankshaft. The next multi-carb engine I'm planning on building will have three Keihin side draft carbs designed for a Harley Davidson EVO engine with 40-something cubic inches per cylinder, on some short home-brewed aluminum adapters bolted to each intake port. Those carbs have a "constant depression" design, with a variable venturi slide controlled by a diaphragm which prevents over-carburetion. The engine I'll be running those carbs on is a bored and stroked 261 with approximately 300 cubic inches. It would be hard to run fast enough to give me a progressive linkage Weber 2 barrel carb of any kind, having struggled to keep one working on a couple of late 1970's Datsun 4 cylinders for many years. The adapters required to fit the Weber carbs to the Fenton manifold will result in a major loss of laminar flow of the mixture and some very bad turbulence just below the throttle plates, also.
One other point, and I'll get off my soapbox for now- - - - -the geometry of the intake and exhaust ports of the stovebolt cylinder head make any so-called "improvement" of gas flow with intake and exhaust manifold modifications the equivalent of putting lipstick on a pig. It's like joining two pieces of tow chain with a paper clip. The cosmetics are impressive, but the end result will be a big, expensive disappointment. "Your mileage may vary"- - - -but the several decades of dyno testing of mild to wild engines that I've done have me convinced that the stovebolt engine has no business trying to run in the RPM range where improved intake and exhaust flow might be benefecial. The laws of physics are not "suggestions".
Jerry
