Converting from stock Gurtner AR carburetor to a Dellorto SHA carburetor

Revision as of 13:49, 5 September 2006 by Davidp (talk | contribs) (grammar edit)

The Gurtner carburetor is an oft-maligned piece of equipment that can function well and supply adequate performance for the motobecane user. It has the additional benefit of being designed to fit and work with the other systems on a Motobecane moped, such as it's controls, and so installation and maintenance is fairly easy. That being said, Gurtner AR's can be difficult to clean after being ravaged by time and the elements. NOS replacements can be difficult to find and pricey, so a number of riders over the years have looked to replacing the carb with a readily available and adaptable Dellorto SHA style carburetor. There is the additional benefit of swapping out a small, fuel efficient, slow carburetor for a larger, 12mm (Dellorto SHA 14/12) or 15mm (Dellorto SHA 15/15) body.

This manual is specific to the Motobecane 50v frame. Adapting Peugeot 102 or 103's or Motobecane 7's will require some adjustments.

  1. Use the "bendy" 14mm intake, available from Handy Bikes or 30MPH parts engines.
  2. Many prefer the click choke model SHA carb body, as the choke slide on the cable choke model never fully closes. Furthermore, the click choke version means that you have one less cable to deal with, which takes up room, requires periodic adjustment, and can be a hassle to deal with whenever you reattach the carburetor after cleaning it.
  3. Cut your throttle assembly so you can pull the cable enough to open the carb all the way and let it close enough to idle. See guide on Adapting Your Motobecane Throttle for a Larger Carburetor.
  4. Use a #57 jet with the metal screen filter and round air cap. Use a 63-65 with a uni-filter or other high flow filter.
  5. Tilting the carb clockwise when looking at it from the moped’s starboard side will keep it from hitting the frame when the engine is fully variating.
  6. Some say using the Gurtner cable guides will help.
  7. If you have a variator I recommend removing 1 or two ball weights in order to utilise the newfound engine speed capacity. See guide on Motobecane Variator Repair and Tuning.