Adapting Your Motobecane Throttle for a Larger Carburetor

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Note: This guide is specific to the Motobecane 50v, although it may possibly apply to other Motobecane models as well.

Swapping out your stock Gurtner carburetor for a larger version such as a Dellorto 14/12 SHA or Dellorto 15/15 SHA is a common modification performed by many Motobecane owners. It is a relatively easy and painless procedure that will provide an instant boost in performance.

If you are switching to a Dellorto 15/15 SHA carburetor, one hurdle you must face is that the Motobecane throttle assembly on the handlebar is only designed to pull approximately 12mm of cable; this is not enough room to pull the throttle slide all the way open in your new carburetor. Fortunately, this problem is easy to fix, provided that you have access to a dremel. This guide may sound daunting upon first read; rest assured that it is actually a very easy procedure.


Steps

Moby Throttle Mod.jpg
  1. Remove the grip on the throttle assembly.
  2. Unscrew the cable end that attaches the cable to the throttle assembly.
  3. There is a very small screw keeping the throttle bar in place; unscrew this and put it in a safe place (small screws have a tendency to get away from you, never to be found again).
  4. Remove the throttle bar from the handlebar, being careful to grab the little piece that attaches the cable to the throttle assembly (another little piece that likes to get away from you).
  5. Look at the throttle bar -- you will see two holes, one which is perpendicular to the throttle bar and is close to the edge of the bar, and one that is diagonal. The perpendicular hole is what is limiting you from pulling the throttle cable further; you will need to dremel this out to make it longer.
  6. Before you use the dremel, make sure to wear safety goggles, long sleeves, gloves, and some sort of face mask or bandana to cover your mouth. Those little metal flakes are nasty!
  7. With the throttle bar facing you in the same position that it would be on the handlebar, cut the TOP portion of that perpendicular hole, extending the hole about 3-4 mm or so. DO NOT extend this hole too far, or the piece that attaches the throttle cable to the throttle assembly may come out too far when the throttle is fully open, and could potentially get stuck at full throttle.
  8. Slide the throttle bar onto the handlebar, and reinstall that tiny screw (it fits in a spot along the perpendicular hole that you just dremeled). Also, put in the piece that attached the throttle cable to the throttle assembly.
  9. Open the throttle all the way and inspect the placement of that little piece -- if this is coming out too far, you will need to fix this...somehow. You don't want your throttle to get stuck at full speed!
  10. Attach the throttle cable, and put the grip back on.