Most carb builders compensate for this by closing the power valve to lean out the mixture as the vacuum increases at higher rpm. Thus when you jet for high rpm the idle and midrange are very lean. At high rpm fuel flows from every orifice in the carburetor whether it is supposed to or not. The main characteristic of these carbs is the tendency to run excessively rich at high rpm. At 7 inches of vacuum the 350 carb is really flowing about 430-440 cfm. A 650 carb on a 358 cubic inch engine will seldom see 1.5 inches but a 350 carb on the same engine will frequently see 5 to 8 inches. 2 barrel carbs are rated at 3 inches of vacuum and 4 bbl carbs are rated at 1.5 inches. Now is a good time to understand carb flow ratings. The same problems exist in the Rochester and Motorcraft carbs but they are addressed a bit differently. The 350 carb is most prevalent in the South and the 500 more popular in the North. They are rated at 500 and 350 cfm respectively at 3 inches of vacuum. Since the Holley 44 are the 2 most popular carburetors used today, this will be the primary focus here. Make no mistake there are very few truly stock 2 barrel carburetors in oval track racing at any level. This article is not intended as a do it yourself article but rather a guide to the modifications required to make 2 bbl carburetors competitive in oval track racing. The 2 barrel carburetor in Oval track racing
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