lioncoeur

Hey guys, I'm new here...just found the sight. I picked up a '76 xs500 recently, not really running. I've rebuilt and thoroughly clean the carbs since purchasing it but haven't done the valves, timing etc. Just took it for its first spin yesterday. It seems to rev fine up to at least 4k (I didn't push further) when sitting at a stop, but when I put the bike under load, that is, try and accelerate away from a stop, the engine stubbles and hesitates above about 2500 rpm. I can push it above but it has no power and runs terribly. But the moment I come to a stop and rev the engine, it'll push past 4k no problem. The floats where set to the stock height (they were a little low before), but I don't now about the jet sizes (how do I tell?) Also, when I re-installed the carbs I put on pods. The bike came to me already equiped with a 2-1 exhaust. Any ideas what to look for, what to do next? I'm new to working on engines, so if this seems something really simple and stupid, my apologies in advance.