Ignition issues...

About the transistor case shocking you, yes that is correct. It is a connection to coil (-). When the ignition triggers, the transistor turns off, the coil primary peaks to about 400V, the secondary winding multiplies it by about 80, so the peak spark voltage about 30kV.
Some say the new units have fake transistor case for show, use TO220 package transistor on inside.
About the pickup gap.The trigger is a change of reluctance. The pickup is biased with a magnet, the reluctor tooth pulls flux away, and as it passes the ignition triggers. The pickup voltage is proportional to rate of flux, the change of flux is related to gap, the rotation speed changes rate of change. Too much gap typically causes starting problems, before it causes running issues. There be other issues...