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ROClarke wrote:I wish I knew what you are talking about,electrickery is not my strong point
Fast n Furious wrote:Take a look at a CDi flywheel and you will notice that 2 of the poles have extended overlapping tabs that form the trigger point of the ignition.
As the flywheel rotates, the first tab induces a positive voltage into the pickup coil. As it passes, the voltage decays back to zero then immediately the 2nd tab passes inducing a negative voltage and back to zero because the magnetic field is inverse to the first one. ( North pole then south pole)
Usually the triggering point is where the voltage crosses through zero, although this does depend on the design of the CDI.
If your stator plate is too far in or too far out, then the induced positive and negative voltages will be imbalanced and this can lead to erratic triggering / timing issues. Sometimes it can be so imbalanced that it won't fire at all. Typically this happens with some mismatches of crank, mag housing and flywheel arrangements. Mostly it occurs from using mag gaskets that are too thick and variations in stator plate construction.
It is balanced when the positive and negative spikes are of equal amplitude. Ideally, this test should be done with the red wire disconnected from the CDI because the impedance of the CDi can vary between the positive detection circuit and the negative one with some CDi designs.
By adding or removing shims behind the pickup you can set this balance for optimum triggering.
Most CDi's will zener clamp this voltage to + and -5v. The amplitude of the pick up output voltage is directly related to how close the magnet laminates are to the pickup head as they pass over it. If they are too close they will give good voltage output but as the mag bearing wears, you run the risk of a mechanical collision with the pickup and that's game over. The scope allows you to determine optimum clearance here.
The pulses between the spikes are where the other 4 magnets induce a voltage into the pickup coil but do not pass through zero and so do not trigger the ignition.
Hope this helps.
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