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This throttle tube reduces rotation by about 22 degrees verses the stock tube. It's not a drastic difference, but enough that going from closed to WOT no longer requires grabbing two handfuls of throttle.
NOTE: The pictures above are of a bike the the Keihin FCR39 carb. The Mikuni BSR36 (stock on the DR-Z400S/SM) requires less rotation to get to WOT.