older carbureted WR, No full throttle

I have this 2003 WR250f, I know this isn't the normal bike for this forum but i know you guys can help. I recently rebuilt the carburetor, and it will run at idle fine with choke on. I turn it off it will very slowly die off. If the bike is in neutral, I can give it 1/3 to maybe 1/2 throttle and it will rev to the redline. Any more throttle and it dies, not more rpms, but actual twist of the throttle. when I'm on the bike, in any gear, I can give it 1/3 to 1/2 throttle, but anything more and it dies. this isn't a "fight to stay going" It's "accelerate, accelerate, nothing" its almost as if i were to hit the killswitch. I changed the spark plug, and the old one was old but fine. the only thing i can honestly think of is I have somehow misadjusted throttle cables or the throttle position sensor has crapped out on me. any help would be greatly appreciated!

Check your pilot jet, sounds like it either plugged or dirty. it handles idle a low RPM

but would that have anything to do with cutting power entirely? the failing to idle isn't really the problem. it really seems as though I've just pulled the spark plug wire off as soon as I go past half throttle. it doesn't glug, cough, almost go, nothing.

I'd replace the pilot jet with a brand-new one because sometime they get so plugged-up with varnished old gasoline, they can't be cleaned well enough without ruining it.
Needing the choke to be pulled up to run is a classic sign of a still-plugged-up pilot circuit.

I'd make sure every single jet, orifice, and passage way is clean and clear.
That's every one.
Remove the fuel screw, too (watch the little O-ring, spring, and washer).

Make sure the accelerator pump is actually squirting fuel when you twist the throttle.
The passage leading to the accelerator pump output nozzle and the nozzle, itself, are more tiny orifices that can get clogged with old fuel.

Basically, the carburetor would come back off and be put back on the work bench for Round No. 2 if that were my bike.
Worth it, because I've owned two Yamaha WR250Fs (still have a 2002 model in great condition), and when they run correctly they're a great dirt bike.

Got that right, dismantle a soak in pinesol for a couple of days and blow all the jets and orfices out with a air nozzel and compressor, I would also buff the slide on my buffing wheel and clean so she works smooth.

If you have access to an ultrasonic parts cleaner that's the way to go. If not a lot of carb cleaner and a very small wire to clear all the tiny passageways will be your friend.

My first thing would be to figure out if it is a fuel or spark issue. Also tight valves will cause some real goofy issues, get a cheap feeler gauge and check them per yamaha service manual.
If the valves are tight your wasting you time, they must be in spec before moving on.  
I had a kawasaki bayou that would not rev, it didnt make sense to me at the time but it was a tight intake valve

Next I would pull the air box snorkel, start the bike, rev it up to the point where it starts to bog and give a small shot of starting fluid into the carb, if the bike revs up you know your starving for fuel.
if it does not your looking at a electrical issue, stator, coil, cdi and so on..

if the bike revs up on starting fluid, the carb is plugged end of story, or there is a leak in the intake (cracked carb boot or bad oring on intake boot)

The idle issue is a clogged pilot circuit, or jet, most people clean the jet by fail to understand the pilot jet circuit or how it works, google this

I stopped trying to fix things years ago that i didnt fully understand, I now research how it works and then tackle it successfully

Pull the petcock out of the tank and see if the screens plugged or gone.

My buds wr400 petcock desolved and caused issues like this, the carb wasn't getting enough gas plus the carb kept getting dirty.