What is wrong with my motorcycle?

I just purchased a 1975 Honda XL250 in good shape with 6,000 miles on it. At the auction the tank was empty and the fuel line was disconnected, so nobody knew if it ran or not. Paid 260 for it, took it home, filled her up and connected the fuel line, and just like that she was running on 2nd kick. Now here's the weird thing. After about 4 minutes of idling or 1 minute of riding, it starts puttering and then dies. After that it won't start for about 10 minutes. Cleaned air filter and fuel filter, oil level is fine too (completely changing this week). Before we take it in, anyone have any ideas what it could be? We assumed it could be the lines are still gummed up or something (we don't know how long it had set before we bought it), or possibly needing some work in the carburetor.

Clean the carberator or rebuild it they sell kits, and clean the bowls on the bottom that should fix your problems.

You could try adding some seafoam to the gas for a while. It works pretty good. But probably, as already suggested you will need to clean the carb completely. Take your time and pay attention to what goes where. Its pretty easy and you will learn a lot about how engines work.