electronic ignition question

[red griff 500]

Whilst checking static ignition timing, I noticed that there was no spark at near TDC when the engine was rotated very slowly - to get a spark I had to rotate it a bit quicker. This doesn't seem logical to me as I think there should be a spark under all circumstances due to the fact that the spark is generated by switching the low tension part of the coil by the ignition amp and magnetic pick-up in the dizzy, and this should not be affected by velocity.

Where am I going wrong?

[shpub]

The sensor requires a bit of speed to register. If it creeps the pickup misses it and won't fire.

[red griff 500]

Thanks Steve I didn't know that - but why should the pick-up miss the switch point, even if it is slow. Maybe the electronic sensing circuit works on rate-of-change of signal rather than absolute signal levels?
Also, does this mean that when the engine is running (i.e. much faster than me turning it by hand ) that the spark is stronger?

Edited by red griff 500 on Monday 4th December 17:01

[GreenV8S]

The distributor uses a magnetic variable reluctance pickup which is highly speed sensitive as Steve says. As long as the signal from the pickup is strong enough for the ignition module to recognise, the module will give you a spark. So in that sense, no the strength of the spark doesn't increase with speed. In fact the reverse is true - at very high RPM the coil doesn't have enough time to fully charge and you can end up with a spark that gets slightly weaker with revs - but that's nothing to do with the signal strength from the pickup.

[red griff 500]

Aha! thanks GreenV8S. I now understand.