I inherited two carburetors with the Basket Case, one belonging to an XR500 motor and one to an XL500, and I am curious what the differences between these units are. Here are my findings.
Both carburetors are piston valve 35mm KEIHIN with a main jet of 150 (factory 155) and a slow jet #55. The model designation is PD11B for the XR and PD07A for the XL. For both units, factory position for the needle jet clip is the 3rd groove and the initial pilot screw opening is 2 1/4 turns.
While rebuilding the XR carburetor I observed only two main differences between the two units:
The XR carburetor has a manual choke lever directly mounted on the left side of the carburetor body while the XR carburetor has a remote cable operated choke with the cable attachment mounted on the right side of the carburetor body (see picture below).
Rebuilt XR KEIHIN carburetor on the left and “as found condition” XL KEIHIN carburetor on the right. Note the choke lever mounted directly on the XR carburetor while the XL has a cable mechanism mounted on the right side (left side of the XR carburetor displayed in the above picture and right side of the XL).
2. Emulsifier tube (needle jet holder)
The XR emulsifier tube has 4 additional holes when compared to the XL. This could be a custom modification done by the previous owner(s) to reduce plug fouling and lean the mixture. Not sure yet, will need to investigate.
Next step, let’s compute the main jet size, jet needle position and pilot screw opening, taking into account average ambient temperature and elevation.