It isn't pie in the sky, but like a lot of things it needs interpretation. First, inductive electronic ignition advance in a nutshell:
The ignition spark is triggered by pulses from the pick up, which are generated by the reluctor pole passing the pickup coil. Increasing the speed the reluctor passes the pickup coil will alter the induced electrical signal in the pickup coil, specifically the pulses get closer together in time! What the advance circuit on the board has to do is detect the signal and trigger the ignition to spark at the appropriate crank angle. (This is why it is always imperative to strobe the ignition timing to see what you actually get across the rpm range until the measured advance stops changing)
What your reference says is that the shape of the reluctor also 'shapes' the trigger signal, but more specifically it is saying that the induced voltage of that signal does not decay as quickly at higher rpm.....changing the point at which the spark is triggered. The signal is the input to the advance circuit on the board in the amplifier.
Reluctor shape may well influence signal shape, it would be difficult to be sure of the specific influence without testing various reluctor forms, which clearly Lucas did. I think there is a confusion also with the wording in this reference:
Which says at 4. 'The shape of the triggering poles on the reluctor are different for Fixed Ignition and Automatic Advance/Retard. It should therefore be noted that a four-stroke Reluctor will not run a two-stroke satisfactorily on Fixed Ignition'
This does not say that the reluctor shapes the advance curve, it says one type or reluctor is suited to a system with an advance curve, and another type is suited to an ignition without and advance curve. Many 2 strokes do not use and advance curve. Note that often on a 2 stroke with electronic ignition the ignition actually retards at higher rpm to avoid detonation!
I would suggest that the RITA reluctor shape really gives a narrower profile running close to the pickup itself which will also influence the duration of the waveform, and if the physical curves weren't added the narrow reluctor ends would also have been a mechanically weak structure! We don't know what influenced Lucas to adopt that particular shape, so we can't discount mechanical strength or production/manufacturing needs as well as ignition advance.
However, the induced signal will change the trigger point with rpm whatever the shape of the reluctor, simply based on the speed it passes the pickup (refer again to bias voltage). And regardless of the influence the rotor shape may have. The advance is electronic and performed by the circuit in the amplifier box.
The actual RITA I owned had a basic square reluctor end so no fancy stuff there and was used with an earlier style of pickup, which required a modified timing cover to mount it. The ignition advance was jumpered out! So it was a fixed ignition type. However, as far as I can see, the advance circuit was present and basically the same as on advance models and later models!
My guess is that the square reluctor and the earlier pickup either gave a somewhat unreliable advance, or simply and more likely, continued to advance as rpm rose above 5000rpm, which is undesirable on any engine.
So the Norton race shop which was the former owner of my ignition either used a fixed ignition unit, or decided to jumper the advance out to run full advanced ignition on a race bike that spent8 most of its life above 4000rpm.
)
). Interesting enough, the circuit diagram in this thread also mentions a mysterious jumper.
