It just means that those looking at the post don't have the answer. I don't either but I can tell you that the resistor plug/sheilded wire thing doesn't make a diference. All my gas engines are that way except the 3w, which uses a shielded wire but a non resistor plug.

None of it makes a difference. I can't obtain consistent rpm numbers with my H-9 tach either. At least from the back I can't. From the front things improve but who wants to stand there at wide open throttle. I've gone so far as to paint a flat black stripe on the back of a prop to see if things got better. They didn't.