I shim all my engines to .030 and run 30% sidewinder worlds. Even my little .12's like to run like this.
I've been told you can run 30% down to .024 shimming but the tuning may get a little temperamental.
Your thumb on the flywheel of an idling engine will stop the engine immediately. Just give it a bump with the pad of your thumb. Works on buggies, truggies, 1/10, everything.
: )