50 hours on a 21 year old bike isn't good. Mainly if the fuel has jelled.. Take the top-end apart, your rings could be frozen.. Your reeds could be cracked, your carb boot MIGHT be leaking. It's hard to say, but I'd pull the top-end apart just to double check.. I'm going to guess frozen or stuck rings.
But all this together, taking the topend apart is a good start.