you might piss off the neighbors evetually without a muffler, or hurt your ears for that matter.... but if you want to clean all the carbon out of the muffler build a nice fire and stick it in. use a tongs to move it around and crap and bang it on some cement to nock lose any crap in there, and then if you have an air compressor blow some air through it to get any crap out. if you really want a free flowing exhaust do a search in the performance forum....
as far as the carb tuning goes you might want to take off the air filter at first because it will likely start easier(you may have to start multiple times) the air screw should be flush with the carb(screwed almost all the way in) you should be able to see 1/2 to the whole head on the idle screw depending on how high you want it to idle... more screwed in is higher idle.
the needle on the throttle body has a little clip on it, and it needs to be in the center position.
the carbs on these bikes need to be super clean, blow some air through all the openeings and then use an inline filter to keep any crap out that could clog it up.
try those settings to start then put the air filter back on and fine tune it, remember the motor has to be warm to hot to idle properly without any choke. use the choke to start and let it run on the choke for 2-3 mins.