Fuel weighs 6 lbs. per gallon. One gallon holds 231 cubic inches. If
we stack all those cubic inches atop one another, we get all 231
cubic inches pressing down on one square inch of surface area at the
bottom of the container. Therefore, there is 6 lbs per square inch of
fuel pressure at the bottom of a column of fuel 231 inches tall.
Dividing 6 lbs by 231 inches yields a usable value of head pressure
of 0.026 lbs per inch of height. So if your header tank bottom
(figuring a nearly empty tank) is 20 inches above the carb needle
valve, then the fuel pressure at the carb is .52 psi or about ONE
inch of mercury. Not a lot, and easily overcome by misguided ram air
Wouldn't that only be true if your fuel line was equal to one square
inch? 3/8" line is quite a bit smaller that one square inch.