FCR's come in two body styles, (as well as differant bore sizes) the OEM style and after market style. The OEM version has the spigot and air boot adaptor cast in with the body. The after market type has a threaded spigot and air boot adaptor that can be removed. However they are put on with red loctite and can be tricky to get off. The FCR's that are original equipment on any of the Japanese bikes are almost allways the OEM style. KTM has a mixed bag of OEM and after market. The good news is that an after market FCR from one bike can be adapted to a different make and model by changing the spigot and boot adaptor which you can get from Sudco. Sudco charges about $50 each for these so your second hand carb has to be cheap for it to stay a good deal. The OEM FCR's may or may not fit from one bike to the next so it's a try before you buy kind of a thing.
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"If it's hard to do, you're probably doing it wrong."