I don't have a raptor but my friend does to me it sound like a fuel problems also which is obvious...I would take the carb apart thoroughly and check it take all of the jets out and use carb cleaner and make sure you can see light through them...also check the diaphram of the carb becuase if that is torn or not seated right it can cause you some pretty big problems...when hitting the gas look into the carb and make sure the butterfly is opening and make sure it isn't sticking or else it will not run right that could be why it seems to run with the choke on...check the throttle cable...try adjusting the idle...air/fuel mixture screw...and check to see if the fuel petcock is clogged or any of the lines...take your hand and put it on the carb and see if it is sucking in at all...hope this is any help to you...have you adjusted the valves at all by the way...or maybe its something stupid like bad gas that happens everyonce and a while...how do the spark plugs look color wise...later
Brett

 

Update:

I finally got the chance to do some work on the quad.
I didn't take the carb apart, but I did spray it out pretty good with carb cleaner.
I took the tank off and the petcock(sp) everything was good.

It started with the choke on, but when you turn the choke off it would die.
I had to adjust the carb plate screw. I turned it counterclock wise and finally got it dialed in to run with the choke off.
I got it were it will idle perfect for a long time and no longer cuts off when you get off the gas.

Only problem I have now is a pop every now and then from the carb. I had it before when the quad was started without the airfilter.
I'm going to adjust the carb plate screw some more to see it that will help or not.