[woodsrat]

I've run one of those Tiny Tachs for years. They sell for $40* and are extremely simple to hook up (you wrap a wire around the spark plug lead). They have their own power and while they're supposed to only last around five years mine is still going strong and I bought it in '03. It would work great on your thumper.

*Apparently they have upgraded the Tiny Tach and it is now resettable for the indicator for maintenance (mine isn't and flashes irritatingly when it says it's time for "Oil-Lube"). It's also more expensive at around $60.