I have a JD 425 Y-Twin liquid cooled 20 hp ohv k series Will start but will only stay running at half throttle with choke pulled all the way out will kill if I pull choke in evertime.

check fluid level in the cooler / radiator that its clean 'air can flow through ' air filter is fuel and carb not cooling system --

Check fuel pump delivery for adequate flow. If when choke enrichment is applied and it runs, then dies when choke is off, fuel flow is inadequate and needs choke enrichment to compensate. Also, if engine dies or chokes when increasing rpms, this will be a symptom of too little fuel. Check fuel flow at pump, then, if flow is good, check for carb blockage, unscrew the jet and inspect, check the operation of the solenoid at the bottom of the bowl, it has a wire attached to it. Trace that wire to where it plugs in, unplug it and touch it to the positive pole of the battery, it should retract. If not you need a new solenoid that has the job of metering in gas to the inner bowl below the jet assembly.

Many have auto chokes, which are set to close and open essentially with spring pressure. You can verify this by looking into the intake, ahead of the throttle plates. Other designs use a priming bulb to accomplish the same function.

Sounds like fuel starvation. Check for plugged fuel filter or sediment or dirt in the fuel tank. Failing that, examine the carburetor for dirt/sedment plugging it. Good luck!

could be air cleaner clogged and/or crankcase ventilation
breather or tube to air cleaner frame work clogged

Sounz like the fuel line / filter is partially clogged.

same problem, was told it was the jets, are your symptoms as follows
runs at low throttle, will only run at full throttle if fully choked
dies if choke is relieved

I THINK THE CARBY NEEDS A KIT AND SOME ADJUSTMENT

SOUNDS LIKE A FUEL PROBLEM OR DIRT WHAT OTHER SYMPTONS DOES IT HAVE