4 stroke XR100 carb gurus..please help!

My 11 yr old bought himself a mint 2003 XR100 this past Xmas.

I have a problem where the bike cuts out as soon as I take it 1 click off of full choke-

Take the bike out of the garage and flip the choke lever all the way up and kick the starter. The bike starts right up on the 1st kick no matter how long it has been sitting or how cold it is outside- it starts, idles and runs fine (on full choke).

Now the bike is warm, you can ride it on full choke (rough in the higher revs), or if you keep the rpm's up you can run it on half choke and it runs great until it comes back down to idle and it stalls- You have to put it on full choke to start and then ride at high idle again.

As a test, I started it up and it idles on full choke, then I move the lever to half choke and it stalls immediately. At half choke I can't even rev it up and keep it running.

Before I open the carb up and clean all the jets, does anyone have any suggestions about the choke?? or is it definately in the jets?

thanks, I appreciate any help!

thanks guys, just wanted to be sure there wasn't more to it.

thanks again!
Greg