Home Forums Tech Talk Mikuni 40mm I-series Carburetor w/ Accelerator Pump CR125 Shifter

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      Robert Horvath

      Subject :

      Honda CR125 / Unlimited Expert Shifter class / Mikuni 40mm I-series Carburetor w/ Accelerator Pump (BN40I 38-27) or (38 – 24 with built in internal fuel pump)

      The Postman just brought my new Mikuni 40mm carb with the built in accelerator pump.

      So with that being said I had to blow off any and all yard work that I was planing to do this weekend and instead try to get this physically large Mikuni carb shoe horned into the small space available on the Honda CR125.

      Unfortunately the accelerator pump mechanism on this particler carb takes up a lot of room in mounting the darn thing in clearing the kick starter bump and chain guard.

      The accelerator pump fuel injector nozzle puts out a very nice fully atomized fine fuel spray just above the throttle butterfly via a variable cam actuated roller in direct accordance with the throttle valve position.

      I think this is as close as Fuel Injection one can get on a Go Kart?

      Here below is a photo of the injector nozzle mechanically spraying fuel directly down the throat of the carb.

      The fuel spray is fully adjustable for duration and volume desired

      No more bogs or hesitation > ever > when coming out of a tight corner and with very low engine RPM !

      The accelerator pump side of the carb

      The accelerator pump apparatus had the high speed mixture needle so obscured that I had to add an extension to the thumb screw just in order to get to it with a glove on. This was a very tight fit to clear everything.

      The modified longer light weight (brass tube) mixture adjustment screw.

      The throttle cable side of the carb showing a 1) The carb to rubber flange adapter (homemade), 2) a Honda RS 125 intake insulator boot and 3) lastly a V force 301 reed cage

      I decided to use the carb that uses a external fuel pump for simplicity,greater reliability and higher fuel flow volume.

      The dellorto fuel pump and three # 4 micro mini worm drive clamps

      As far as performance goes …..This carb took a consistence 3 tenths of a second off of our best ever lap times on our local short, tight twisty 6/10 mile sprint track.

      Just one of our Mikuni carbs in action on Craig’s Shifter at Road America

      2014 Road America at Elkhart Lake Wi. Seasons (Unlimited Expert class) Go Kart Shifter Championship Won By # 92 Craig Hemmen on a 2014 Praga Dragon Kart > Tuner / Mechanic Bob Horvath > Honda engine Mods by Eric Gorr of Forward Motion.

      Thanks Bob

      Robert Horvath at
      W352N6446 Road J
      Oconomowoc Wi 53066 U.S.A


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