I´d suggest having a qualified mechanic look at it. Among anything he recommends looking at, I´d ask for a compression test and to check valve clearances. I lost one of these in pristine condition due to the disintegration of the exhaust valves on #1 and #2 cylinders. I was having problems similar to what you describe, and the mechanic I took it to first was not a motorcycle mechanic, but an automotive mechanic doing me a favor (he had the same bike for years.) I asked if a compression test would tell me anything, he figured it was something else. I rode it across country and the valves went on me. The mechanic I took it to told me the bad news, and it was due to improper valve clearances (or timing, can´t remember for sure,) maintaining the exhaust valves open partially into the combustion stroke, causing etching and eventual failure of the valves. It basically needed a new engine, (really just the cylinder head, but the engine needs to be removed to replace it, and the time to replace the cylinder head really suggests to just put a good engine in.)