Carburetor idle screw

[Alan Gee]

OK my gas tank looked like it had Corn Flakes in it. Removed the tank etc cleaned it de rusted it blah blah blah.
Clean out the gas line and glass fuel bowl, replaced the non existant bowl screen but some stuff still found its way into the carb. No big deal. took it apart cleaned everything and was impressed by how little was in there. 99% of the stuff was stopped by the inlet screen. OK everything soaked in carb cleaner and cleaned and blown out with air and thin wire poked in all the little tubes.
I put it back and it starts and runs just fine. Just for morbid curiosity I tinkered with the idle mixture screw. I turned it all the way out and IN and it made no difference in anything. How can that be? I took it out to see if it was groved and it looks good. ????

[Bob McCarty]

Alan, That screw is more for the transition from low throttle to full throttle. Start with it out 1 1/2 turns. Move the throttle from low to high and see if the engine revs smoothly. If not adjust the screw 1/4 turn at a time until you find the sweet spot. It may need to go either in or out.

Bob

[outdoors4evr]

If it is not getting enough fuel, then it is getting too much air, so turn the idle screw in.
If it is getting too much fuel, then it needs more air, so turn the idle screw out.

Is there a way to determine whether it needs to be turned in or out?
So if the tractor stumbles when accelerating (from a low to high rpm) then the tractor is probably not getting enough fuel?