Carter B&B Updraft Carburetor Rebuild

Dissassemble Carburetor

  • Remove screws which hold upper body and lower body.
  • Lift off the upper body and pump assembly.
  • Unscrew float hinge pin and lift out float and float needle.
  • Remove main jet inlet valve, pump, check valve and economizer valve assembly
  • Remove the main discharge nozzle.
  • Remove vent tube.
  • Remove step up piston plug, piston and spring.
  • Remove idle passage tube.


  • Soak parts overnight in a bucket of carburetor clean (any parts store brand)
  • Wash with hot water to remove all chemicals.
  • Blow out all passages with compressed air.
  • Pay special attention to the step up rod parts. This must operate freely.
  • Using thin wire clean out the ethanol residue left in the carburetor. Be careful not to enlarge the holes.
  • Test the float by immersing in hot water. As the inside of the float heats up and expands, any hole will show up with bubbles.

Ready for your Carter B&B updraft carburetor kit.


  • Reverse the disassembly instructions.
  • The pin end of the economizer piston rod should be inserted in the economizer valve assembly.



A customer is working on a B&B updraft carburetor. We supplied a kit which does not have the 2 gaskets that go on the venturi. The parts are illustrated in the photo attached. #15 venturi gasket upper & #47 venturi gasket lower.

I’m not sure these gaskets are really needed anymore. What do you think?


In a word:  no.  In 20+ years of restoring BB updrafts I have never even seen those gaskets in a BB, much less replaced them.  In some updraft carbs they are critical, but evidently not in this one.