So by adjusting the idle screw on the carb, it will help the tractor idle better in the idle position but not at full throttle?
The idle screw setting has nothing to do with full throttle. So I understand your questions better, here is how I view throttle positions:
Idle: The slowest RPM the engine will run. The throttle is all the way down, and the engine is running at a slow speed. Loads of any kind are rarely imposed on the engine while it is idling. Like when you are off the tractor, and do not want to shut it down. Generally, the PTO is off, and the tractor is in park/neutral while idling.
Full Throttle: In most cases this is the working throttle position. The governor keeps the engine speed constant no matter how much load is imposed. Unless the work load excedes the rated horsepower of the engine, the engine should always stay at the RPM set by the governor. Always cut grass at the full throttle position.
Part throttle: Any setting between "Idle" or "Full" The engine runs at a slower speed than full, but produces enough power for slow driving, or maybe pulling a tow behind attachment. Part throttle is also good for faster warmup on the water cooled engines.
A sure sign of a properly tuned engine is when it runs smooth at any throttle position, maintains a constant RPM, And has a nice smooth idle! When carburetor issues are present, (Such as plugged idle jets.) the engine will surge up and down constantly. It may surge less under load because of the governor opening the carburetor throttle to compensate.
An engine that is idling too fast is an indication that if it were set to idle nice and slow, it would stall or surge badly. Or the throttle control is not properly set up.