I'm converting a one-lung 4-stroke portable generator from gasoline to natural gas. One thing I need to do is to lean it out to get max rpm under load, so I need a tach.

What I'm thinking is that I can wrap a piece of wire around the spark plug lead to get an inductive pulse. I can clip my frequency reading DVM to that lead and ground the DVM to the engine someplace. Then I can read RPM directly. Even if it's a two-spark per rev engine (which I don't know) it really won't matter, it's just that my reading won't be true RPM but it won't affect my finding a maxima.

Any thoughts? Am I missing the boat completely? Thanks for taking the time to read this.

Charlie