Stalling Issues

[odie]

I have a '01 GZ with 10,625 miles that I bought used. I had fixed it up and it had been running good up until now. I had taken the gas tank off to get rid of some dirty gas and when I put it back on it and refilled the tank it had trouble starting and running. It will start and idle with the choke on for a minute or so but then it dies. With the choke off it will stay running if you give it some throttle but when I ride it and I roll off the throttle to slow down, it dies. I have heard that of air flow problems can cause such issues and the bike does have a gap where the exhaust pipe bolts screw in due to a crack from the previous owner and so the exhaust pipes won't completely tighten; however this hasn't really caused any trouble before so I was wondering if this had anything to do with it or is something else wrong?