Jetting?

I suppose my bike needs to be rejetted. It came from California, and I live in Mississippi, so that's probably one reason. It's been uncorked and has Big Gun exhaust, but a stock air filter. I usually start it on full choke, and have to move it to half choke quickly before it dies. I think the average person would say it runs perfect, but anyone who messes with bikes can tell it's got a tiny sputter. It hesitates if I try to take off quickly, and yesterday it stalled while taking off, then didn't want to start back up. I had just ridden it 5 miles to a gas station, and I had to half choke it and give it gas so it wouldn't die, then took it off of choke (still giving it a little gas), and I took off and rode home. It idles, has never needed a little throttle to stay running before until that moment. And another thing, if it's idling and I back up, it dies after rolling backward a few feet. If anyone can think of any other reason these hiccups may have occurred, I'd appreciate the feedback. And as for jetting, does anyone know which way I need to go with it? On a side note, it had emissions equipment, but it's been removed, and I don't know if it has ever been rejetted, or if it was done prior to or after the aftermarket exhaust was added.

Remove the carb and clean it out...check what's in there... jets etc ?
Here's our guide to doing the job
http://www.xr650r.co.uk/service/carb/carb.shtml