WOW !! never heard of a Black & Decker 21 HP ! Did you mean BRIGGS & STRATTON ..??
you can set the "air-gap" on the flywheel/ignition coil ......
engine timing is alignment of crank-shaft and camshaft but that's internal ( usually only set during RE-BUILD
but maybe, you mean valve clearance, lash, or timing ( all the same )
here's a video of setting the valves, IT'S NOT a JOKE ... he's sort of a comedian, but a very smart TECH. watch ENTIRE VIDEO !!
