Andy is correct, the Bing models that Stihl used were reliable and good performing carburetors, and just about the easiest to rebuild also. The Bing 47 is the 038/038 Magnum carburetor and they are great in that application. The Bing 48 was the one used on early 064s. I've never seen one on an early 066 but I'm sure they were used there also.
Like Stihltech said- kits are spendy for the Bing 48- around $42.00 a pop. The 038 Bing kits are as common as a kit for any Tillotson/Walbro and can be had from the supply stores cheaply. Like Stihltech also mentioned, you have to adjust the height of the inlet needle leve by moving the needle seat, because the lever is made of plastic and cannot be manipulated.