Home Forums Shifter Karts Mikuni 40mm I-series Carburetor with built in Accelerator Pump (BN40I 38-27)

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    • #46061
      Robert Horvath

      Hello again Shifter Friends,

      Subject :

      Honda CR125 / Unlimited Expert Shifter class / Mikuni 40mm I-series Carburetor with built in Accelerator Pump (BN40I 38-27) using an external Mikuni round pulse type fuel pump.

      This just may be the most practical 40mm Carb for somebody like myself to use on a Honda Shifter considering the Mikuni has fully adjustable external high and low speed mixture needle screws….. No jets to change ever….So nice!

      The acceleration on the stand is just incredible due to the built in accelerator pump !

      No waiting for the fuel to be drawn up the capillary metering tube with the engine vacuum (which is not much on a super tight corner)…It just squirts fuel down the throttle bore with a mechanical diaphragm activated by the throttle blade.

      Coupled up to a Honda RS125 almost straight boot intake manifold and a modified air flow guide for the V-Force 301 reed valve cage it makes for a super clean installation.

      This Carb always has a super smooth and steady idle  and easy starts due to the accelerator pump system….no priming or choke  is ever needed.

      The idle speed thumb screw is easy to get to being right up in front and on the left side of the carb.

      Here are some photos of the install below:

      That black box mechanism located under the air box is the 60amp electronic shifter servo for the paddle shifting system selected at the steering wheel itself.

      That makes shifting a breeze!

      For more reading and photos on this great Mikuni carb see my other post on ekartingnews.

      Link :



      Thanks Bob

      Oconomowoc Wi 53066 U.S.A





    • #46504
      johnny brooks

      Your testing of various ‘alternatives’ has been fun to follow and I know many share your dislike of jet changing.
      I am curious as to whether you’ve heard of the APT Smartcarb. It is a single metering rod style of float carb with an ‘auto’ compensation circuit for air density. It can’t be tuned ‘on the fly’, but once dialed in thru rod height adjustment and idle screw it compensates for any air density changes.


      I currently run a 38mm cast model (they also make them in billet) on a Swedetech 5 degree offset boot thru a VForce 3 reed, fed by Dellorto pump (no tee/return). The rest of the motor is Stock Honda as I was not looking for the fastest, just ease of use. This is on an F125 laydown so Stock Honda rules are not applicable.

      Just an FYI for those looking at options.

      • #46553
        Robert Horvath


        No I never heard of the APT Smartcarb. Thanks for the link. I like what they say  about the Carb on there website. I’ll have to ckeck it out further.

        And your setup looks pretty cool too.



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