Motorcycle smoking?

I recently purchased a 1981 Honda CM400T that I knew needed some work. I went through the carbs and it now starts great, but doesn't idle very well as I can't keep the RPMs high enough to keep it running. I am not as worried about that as I am about the fact that after taking it for a short drive (1-2 miles), there is smoke coming from the exhaust where it leaves the head and moreso from underneath the bike around where the exhaust comes together into the muffler.What's wrong with this bike? I am thinking a bad ring but I am not really sure...Thanks in advance!

More then likely, the rings are carboned up after 20+ years of use, and you're getting blow-by. Not a huge deal as long as you don't mind filling up on oil everytime you fill up on gas and replacing sparkplugs much more often.The RPM issue could also be effected by this as oil is more then likely coating sparkplugs. Aditionally, every motorcycle carb i've ever seen on bikes that old that"need some work", need some major tuning/cleaning work.