I've never had to do it myself, but there are many references to cleaning out a clogger muffler or chamber by heating it up real hot to get the internal crud to burn out and a good hot BarBQ seems to be a preferred method. Perhaps you can use the search feature to look up various ways to clean a clogged tailpipe. The choke is a separate cable operated device to change the carb mixture while you are trying to start your engine. My FA50 with it's perfectly clean carb and brand new exhaust still needs a little choke applied to get it to fire up esp. in cool weather. The sequence that works for me is to first prime the fuel bowl by putting the petcock lever in the "Pri" position for about a minute or two, then switch it to the "On" position. Turn on the key switch, set the choke lever all the way to the left, squeeze the left brake handle and start stomping the kick start lever about a half dozen times. If that doesn't work, then gradually move the choke lever to the right while continuing to kick start. If this doesn't work for me, then I start checking around for problems ie. fuel flow and spark. Good luck.