Have you ever wondered why the float level isn't the same for similar carburetors used for different engine applications? For instance, the same large-bore Rochester 2 barrel casting is used for 305 and 350 Chevy V8's, but the float level for the 305 is set WAY higher. The difference is the velocity of the air through the carburetor venturis. The 305 draws less air through the carb for any specific RPM, resulting in less vacuum at the venturi stack. There are differences in the jet sizes and power valve settings, but if the 350 float setting is mistakenly used on a 305, the engine won't get out of its own way because it's running so lean. Set the float right, and the lean surge, power loss, and backfiring goes away.
Jerry
