For some reason, after I get my 1982 CX500 up to 50-60mph for a decent amount of time (5 minutes), when I slow down my clutch is very tight and difficult to pull in. I just had to pull off the side of the road, where I stalled. When the bike was off, the clutch was still sticking an very hard to pull in. As soon as I started the bike back up, the clutch loosened up again and I was able to ride. Not the first time this has happened, it happens at least once every time I ride. Any thoughts on what the problem is and how to fix it?