20 watt c scooters, cooters racing.
The Stock 47cc Carburetor uses the 0.64mm Jet.

                      47cc Pocket Bike Carburetor $30  Pocket Bike Parts

 Specs: 47cc Carburetor for Pocket Bikes.  The stock carburetor has 12 mm hole, the Modified
    Unit Price Part Name Shipping Cost Total Shopping Cart  |             carburetor has been ported out to 14mm.  Plus it has a big jet.
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1

 |$30 47cc Pocket Bike Carburetor |$5 (U ) | $35

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2

 |$30 47cc Pocket Bike Carburetor |$6 (US ) | $66
 

 1

  $50  Modified 47cc Pocket Bike Carburetor  (Ported out 14mm) with free jet pack(0.66 mm, 0.68mm, 0.70mm, 0.72mm  jet)  $5 (US )  $55
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We only sell to USA & Puerto Rico Street address.  We no longer take international order. 
Bigger jet doesn't necessary mean better performance. You pick  jet size
base on the climate.