The tach I want to use is electronic. Connections are: 12V power supply, one input lead to ground, other input lead connects to the negative side of the engine coil, and a slide switch tells the instrument how many cylinders the engine has (in this case =4). The tach just counts the pulses, knows the number of cylinders the engine has, and provides a readout to the analog meter. My thinking is, if I could just "double" or "triple" the number of pulses the input to the tach "sees", it will indicate a higher RPM on the scale (thus indicating 4K RPM for an actual 2K RPM from the engine, making the instrument more sensitive). The engine typically runs at 1200 to 1400 RPM at full load. If this does not make sense, let me know.
P.S. ~ Simply doubling the output reading would be fine.