About 0.010" or 0.012" is pretty standard as the correct air gap for all of the common engines. Most people just use a visiting card (usually about 0.012"), because if you use a feeler gauge it will stick to the magnet unless you make sure you aren't on that part of the flywheel.
I recommend that you never hold the end of a plug lead and turn the flywheel unless you turn it very, very slowly with your fingertips to check ignition timing. Holding a plug lead when the starter is being pulled is likely to do you harm - at the very least it will spoil your day. It creates a current path from one hand to the other, right across your heart muscle. You are applying your own defibrillator just when you don't need one. Fortunately with a small magneto the energy discharge should be lower than a real defibrillator, but it is a very dangerous thing to do, and pointless as well. The purpose of the ignition system is to create a spark, not to electrocute the mechanic, so the only useful test is whether it creates a fat blue spark.
ha ha ha yeh i know its pointles but it wont do me much harm cause im pretty tuff any way i do relise its stupid and they do make testers for that reason but i have diagnosed a few week coils by doing it that way and im pretty far into old school electronic engenering and i have copped a few whacks of 240v ac in my time pluss a few thousand volts from an old tube tv i was working on blew me across the room and put me in hospital.. i tell ya what the must of been a fair few amps sitting in those old capacitors just waiting for me ... but your body does store electricity and you do build a tolerence belive it or not.... but hey any of you guys got a proper spark tester you dont need send it my way otherwise im still happy to just stick my finger in there
hey we all do it redneck style sometimes
