That air gap thing is also important on small engines with magnets in the flywheel to power up the magneto ignition. It's surprising how much better an old Briggs & Stratton engine starts and runs if a 3X5 inch index card is used to set the air gap between the flywheel magnets and the ignition coil pole shoes. I actually learned that trick from a kid who was competing in a high school technical skills contest that I was judging about 30 years ago!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!