If you have normal fingers you CAN take a feeler gauge out of the pack & put a 90 in it about an inch back from the rounded end & scoop a "ski tip" in the end. Then, by leaving the nut loose & screwing the adjuster down( Yep, loosen that sucker up_), you can get a feel for the force required to slip the feeler back & forth. Hold the adjuster with a screwdriver, so it doesnt tighten down as you tighten the set nut. That May loosen the adjustment off a bit, as the adjusters threads get lifted tight into the rockers threads. If so, loosen the jam nut, barely turn the adjuster tighter & try again. Do it till you win.

Have a magnet handy if you drop the feeler gauge. Ive cut mine off short, so its got about an inch, then a 90 & it goes up about an inch or so,bending to accommodate my hand then its cut off.A flashlight is never a bad idea.

Before the spark plug comes out, a blast of air to clear any crud can keep sandy gritty crap outta the cylinder..