[Cal Metal]

The Bergs are truly 58mm and they make the IDA look-a-like in many iterations including 52, 54...., venturi size. The Berg carbs use standard Weber parts (idle jets, etubes, etc). The circuitry for the gas flow is somewhat different; the throttle shafts are sealed ball bearing (I think). The aux venturi is designed for optimum low speed performance, too. They are outstanding carburetors that perform better than a standard Weber. Berg, an expert in VWs, developed the 58mm on four cylinder VW engines.