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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Power Arc Ignitions
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<blockquote data-quote="Oldhaven" data-source="post: 110557" data-attributes="member: 2879"><p>The Vincent Power Arc ignition, (VPA), uses an optical encoder and has a slot which is set at TDC on the front cylinder plus others on the periphery which determine spark events. Even when supplied with power after the ignition is switched on the coil(s) will not fire until the TDC slot is first rotated past the reader on the kick or starter. The coils fire at this first TDC and now that the ignition knows the flywheel position the next and subsequent triple sparks occur at 10, 5,and 0 BTDC on the firing strokes unless programmed otherwise. If the engine does not start on the kick or starter the encoder wheel stops rotating and the ignition resets in microseconds to its initial state waiting for the TDC slot. This prevents loss of encoder position should the flywheels roll back against compression or due to backfire. I have gotten an occasional back fire if my old leg doesn't give the pedal a full stroke. I would guess that a starter, with its more positive rotation, might not do this if the timing is correctly set, unless some other factor like fuel causes a problem. The VPA ignition has so far not been used with a sprag starter, so I can't say how that would go, but a backfire caused by switching on is extremely unlikely, and I have never had this happen.</p></blockquote><p></p>
[QUOTE="Oldhaven, post: 110557, member: 2879"] The Vincent Power Arc ignition, (VPA), uses an optical encoder and has a slot which is set at TDC on the front cylinder plus others on the periphery which determine spark events. Even when supplied with power after the ignition is switched on the coil(s) will not fire until the TDC slot is first rotated past the reader on the kick or starter. The coils fire at this first TDC and now that the ignition knows the flywheel position the next and subsequent triple sparks occur at 10, 5,and 0 BTDC on the firing strokes unless programmed otherwise. If the engine does not start on the kick or starter the encoder wheel stops rotating and the ignition resets in microseconds to its initial state waiting for the TDC slot. This prevents loss of encoder position should the flywheels roll back against compression or due to backfire. I have gotten an occasional back fire if my old leg doesn't give the pedal a full stroke. I would guess that a starter, with its more positive rotation, might not do this if the timing is correctly set, unless some other factor like fuel causes a problem. The VPA ignition has so far not been used with a sprag starter, so I can't say how that would go, but a backfire caused by switching on is extremely unlikely, and I have never had this happen. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Power Arc Ignitions
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