Some transmitters also have a 'throttle cut' option which is a separate button that closes the throttle all the way thereby stopping the engine. That way you can pull the throttle stick back all the way and the engine will idle but will not quit. Pushing the button stops the engine.

Adjust the physical linkages first to make sure the servo can close (and open) the throttle 100%, then make adjustments to your transmitter so it operates to your preference.