I flew my new Raptor 30 ARF for the first time yesterday, however I'm having a major gravity fuel feed problem.

The tank seemed high to me from the start, but I figured being an arf it'd be okay. NOT THE CASE! I fill the tank and by the time I'm ready to start the heli, fuel is pouring out of the carb.

<are you using a fuel cutoff?or a device to keep the fuel from going to the carb while fueling??>

It runs great on a half tank, but I can't get it to do the whole thing.

<Are your fuel lines hooked up correctly?Muffler pressure tap to your fuel tank is fine?needle valve adjusted for break in?no leaks at the fuel tank?fresh fuel?>

I installed a header tank, but it just feeds right through it giving me crappy starting, and a super rich mixture. Is this a common problem and whats the best fix?
<assuming your throttle curves and pitch curves are close,have you tried to adjust the "idle" or "low end screw"/"needle" on your carburetor?,

Just some ideas,its kind of hard to diagnose a lot of things without being able to see the machine or hear it.If theres some experienced heli pilots near you, you may want to catch up with them, and find some experienced help.Most heli guys are usually more than happy to help each other out.It can save you a lot of time,and will help you learn more about heli setup that the manuals wont show.
Check out the pilot locator site,and have fun!