killjack,
The pulses per revolution is one because this is a wasted spark system. However, for some tachs that is confusing because if you look at a conventional single output coil, like the stock points system, the pulses per revolution is one per every two revolutions of the crank. One pulse per revolution is also what a two stroke engine would have.
So, the XS650 looks like a single cylinder two stroke engine to the tach. However, most modern day automobile engines are also wasted spark, so somewhere in your instructions there should be a setting for a modern automobile engine.
However #2: A lot of tachs are made for the conventional distributor type of ignition and in that case you might try the 4 cylinder setting because a four cylinder engine with a single output coil and a distributor has one pulse per revolution when measured at the single output coil.
However #3: The waveform for an electronic ignition is very different than a points type of ignition and some of the cheaper tachs will not work properly with an electronic ignition regardless of what you do.
