My motorcycle just got an upgraded ignition timing method. This new method fires the spark plugs twice each cycle which in turn increases the RPM * 2 according to the tachometer.

Is there a way to half the amount of outputs the sensor is sending to the tachometer? Its been a while since I've done anything with electronics so I was looking into d flip flops to throw out every other output but I don't know how hard this is to recreate on a 12-15v system or if there is a simpler solution for my problems.

Wiring diagram, wire in question is red

Explanation of wiring diagram numbers

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    Do you have any information or schematics regarding the tach sensor? It obviously works off of some firing sequence, but the signal path/level is going to be important.
    – Ron Beyer
    Commented Jul 29, 2020 at 15:13
  • The tachometer uses the right ignition coil to determine the RPM. I have some wiring schematics but those would be a pain to scan. Commented Jul 29, 2020 at 15:27
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    New dial for the tacho would be the laziest approach given that schematics are such a pain to reproduce.
    – Andy aka
    Commented Jul 29, 2020 at 15:39
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    @Bort the origonal images were too big, you can switch any imgur image by adding s m l suffix on the end of the filename
    – Voltage Spike
    Commented Jul 29, 2020 at 16:52
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    If the dial is just a magnetic coil connected to a spring mass system, it might not be counting pulses at all. It might just be a volt meter which measures the average voltage of the pulse train (spring mass acting as a leaky integrator / low pass filter). In that case, you can measure the resistance of the coil (while the dial is stationary so that back em is not present) and add an equal resistance in series so that double the the number of pulses with half the voltage now reads the correct rpm. Old school dials are just elctro mechanical voltmeters/ammeters.
    – AJN
    Commented Jul 29, 2020 at 16:59


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