I wanted to aknowledge David at KDI repros for his quality air filter and boot.  I ordered both for my CT1 and received them in 3 days!  The boot fits slides very easily on the carb, and the air filter construction is much sturdier than the one I had - I'm not sure if was the original, or a Yamaha replacement from Yamaha.  The one struggle I had was that the rubber on the sides of the air fillter is pretty thick and getting the screws in the air filter plate took some effort, but that could be fixed by shaving a little rubber off (I didn't have to do that).  It's a very high quality product and I recommend it to anyone looking at getting an air filter for there early Enduro.