one more thing, if it runs better with choke 1/2 way out,
that normally is a indicator the carb is stopped up.
I have tried this before, have the tractor motor running as fast as you can then pulling the choke closed, keep it closed until the tractor almost stalls out, then release the choke and let the motor increase rpms again,
sometimes if you do this over and over, the carb will pull the item that has plugged the carb on through. but do not place money on this working, but at this point its worth a try.
others may think this is not a good idea,