If a bike isn't running right whether it's blowing smoke or not responding there's just so many variable of what it could be. Carburetors needing adjusting, rings gone bad, exhaust leaks the list goes on and on. Instead of chasing theory's start with the basics and after referring to your shop manual and obtaining the factory specifications for compression on your engine, test it. It will help you in your trials tremendously, trust us we've been there!
This kit from Motion Pro seems to be a great one to start with for small shops. It's made from good quality components and has the three most common sized spark plug hole adaptors- 10, 12 and 14mm. We use it often and so will you if you start wrenching on these old girls!