top end is probably gonna be a must on a bike that old, and if nothing else, take it apart, closely inspect and measure the piston and cylinder, and replace the rings. get a dealer service manual, if you look around, sometimes you can find one to download for free off the internet, but I have found a service manual much, much more helpful than a clymers. I would take the carb all apart, clean it out good with carb cleaner and compressed air, and you may or may not need a rebuild kit (I dont know how common these need to be done). for the exhaust, I would take the silencer apart and repack it, since it sounds like it is filled with black splooge (a little can be normal, but excessive amounts indicate the bike is running rich). once you repack it, I would not ride it much until you get the carb cleaned/rebuilt/jetted correctly, or you will just refill your new packing with new black splooge. once you get the engine worked on and put back together, make sure you properly jet your bike, look for sparkeys jetting guide, and get your bike jetted according to that, it will make a big improvement. thats all I can think of for now, someone correct me if I said something that is incorrect, I am still learning myself,
Jim