how do you test for spark?

[Lyle Seaman]

All I've ever done is (b).  If I don't see decent spark, then it scarcely
matters whether another technique would show some weak spark -- it's clearly
not good enough.

> a) I have one of those little spark testers that let you
>     turn a bolt to adjust the gap.  How big a gap?
>
> b) Failing that (if I can't find the little tool), I'm going
>     to pull a wire at the plug, insert a spare plug into the
>     wire terminal, ground the plug, and then crank it.