A DC volt meter (especially an analog meter) is designed to measure DC voltages by indicating the steady current flow through the meter. This steady state current flow through the meter is very small (sub mil-amps) but is required to deflect the needle. Anything else is undefined.
If the needle was deflecting from EMI (Electromagnetic Interference) then that would be energy radiated by the motorcycle and coupled into the leads of the voltmeter. The leads would be acting like an antenna. Since the phenomenon requires one lead to be grounded to the frame, I doubt this is the case.
While it is really only wild speculation, there are obviously current pulses (what the meter reads) flowing related to the change in potential between the bike and the ground as the motor cycle charges. So this represents charging doing any further quantification seems pointless. The measurement is not calibrated in any way as the meter is calibrated to measure constant voltages.
One would be well advised to spend time measuring voltage drop and cleaning grounds rather than conjecturing on what causes the needle to bounce.
The sparking that is common at the coils is a result of high impedance secondary components. This is usually bad wires. What happens is the igniter controls the primary current buy allowing current to flow and then stops the flow by opening the current path in the primary. When there is an attempt to stop the flow, there is a rise in the voltage across the primary which is further amplified in the secondary portion of the coil. This energy flow between the primary and the secondary is basically like a transformer. When there is current flowing through a wire, then there is a magnetic field. If there is a magnetic field around a piece of wire then current will flow. It is a sharing of the magnetic field between primary and secondary that causes the energy transfer.
So now if you have a high impedance wire (bad wire), the energy that gets launched when your igniter fires the primary cannot fully get to the spark plug as a portion of the energy bounces off the high impedance block. That energy reflects back up the coil wire and ends up arching across the primary leads.
At this point I'm not sure if it is coupling back into primary through the coil or just arching over but the effect is the same. Regardless this has nothing to do with charging and all to do with bad secondary ignition. Since we already know the phenomenon in 1.) above requires a connection to the bike frame we know that it is not EMI from the ignition.
No that I suggest this is a good idea, but if anyone was so inclined I suspect if you disconnect the R/R and start your engine that you will probably not see any bounce or at least a different bounce.
and has to do with shared magnetic field between the current flowing in the primary with the magnetic field of the current
charging and all to do with bad secondary ignition. Since we already knwo the phenomonom in 1.) above requires a conenction to the bike frame we know that it is not EMI from the ignition.
No that I suggest this is a good idea, but if anyone was so inclided I suspect if you disconnet the R/R and start your engine that you will probably not see any bounc or at least a different bounce.
and has to do with shared magnetic feild between the current flowing in the primary with the magnetci feild of the current
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