Carburetor: The Holley R4412 unmodified. All carburetors must pass track supplied gauges. The only changes that will be allowed are as follows: The choke plate and shaft may be removed, jets, power valve, accelerator pump cam and accelerator pump discharge nozzles may be changed. Idle holes may be drilled in the throttle plates. Throttle plate screws may be trimmed flush with the shaft. No other changes allowed. No reshaping, polishing, grinding, machining or drilling allowed. No adjustable (jetted) air bleeds or circuits. Gaskets must remain unaltered.