How does the ignition advance work?

[Fazerider]

Generally the Speed Sensor and TPS control the advance of the timing. When the engine is revved, but bike is not moving the timing variation is different as to what it would be when under load hence the requirement of the speed sensor, TPS and the rev counter to work together. The timing changes depending on the TPS position when not moving but has a different setting when at the same throttle position but on the move and the revs and speed are up. The would changes the torques levels also by varying the timing as a given speed throttle position, engine revs and speed. The system in the fazer is basic compared to the later systems in bikes and cars since it has carburettors and it cannot change the fueling.
Newer designed systems for fuel injected engines can vary the timing and fueling dependent on throttle position, vehicle speed, engine revs, air flow, temperature and a few others. The torque levels can be varied by the advance or retard of the ignition and fueling depending on the values detected from all  sensors.
The reason Fazerider probable noticed no difference was that signal stopped because the rotor broke and it would appear to the ignitor that the bike was not being ridden. If the cable was cut then the ignitor would see it and throw up an error signal to the Rev Counter, however an intermittent fault to the cable could cause a misfire or rough running due to the constant variation of the timing the same as worn tracks on the TPS does.

Hope that makes sense  :rolleyes

Well, not to me. If the revs are high and the TPS sees a small opening angle then the ignition controller knows the load on the engine is low.
Conversely, if you're thrashing up through the gears at max throttle, why would ignition advance need to be different in 6th as opposed to 2nd gear? If the Fazer employed a ram-air system to pressurise the airbox it might make some kind of sense (though not as much as having an air mass sensor), but the intake is from a zone of still air.
I’ve had two issues with the speed sensor. The first was when the sensor itself died and  the speedo registered 0 mph at all speeds. The second was when a clumsy mis-routing of the cable caused it to rub against the brake rotor bolts and the speedo needle randomly jumped around from endstop to endstop.  I didn’t experience any change in engine behaviour on either occasion.