1984 atc250r pulse generator theory

[Tc_01]

Hello,
I have some questions about the understanding of a pulse generator on a 1984 and earlier atc250r.

I believe I understand how a pulse generator works but these earlier models have me scratching my head. Its mounted under the flywheel, attached to the stator, and i imagine it picks up a signal from something on the flywheel in order to send the signal to the cdi so it knows what position the crankshaft is at, but i dont see anything on the flywheel which would tell it what position its in.

Everything i see is on it is identical, anybody know what these pulse generators are looking for?

[wonderboy]

It is just another coil of wire that generates an electrical pulse when the magnets of the flywheel pass by. It is the exact same principal as the lighting coil, just on a smaller scale. The placement of the pulse generator is designed such that it generates the voltage at the proper point in the cranks rotation.

[wonderboy]

If you are digging into the physics of the situation, read this:
https://en.wikipedia.org/wiki/Electromagnetic_induction

Basically, if you move a wire through a magnetic field, or in the case of our motors move a magnetic field across a fixed wire (coil) you will generate electricity.

The pulse that triggers the CDI is just an electrical signal generated by the magnets in the flywheel acting on the coils inside the pulse generator.

[Tc_01]

Thanks for the info Frank. I guess what im having trouble with is that I understand that the pickup coils on alot of other machines are small magnets and there is usually one spot on the flywheel which has a metal ridge or something similar and that is what the pickup coil picks up on. But all the magnets inside this flywheel are symmetrical, along with everything else inside the flywheel, so that is why i cant understand how it is able to tell where the crank is at in its rotation

[wonderboy]

The system you described is how a hall-effect sensor works. Hall sensors can either detect a metal tooth moving by, or detect a magnet depending on how the hall sensor is configured (magnets will typically be needed somewhere in the system). Cars use this method of tracking the crankshaft rotation (cams shafts and wheels too).

Although they would work, I'm pretty sure out engines don't use hall effect triggers, at least not the 350X or 250R. I think they just get a simple pulse of electrical energy generated by the pulser coil as the flywheel magnets rotate past.

Even though the flywheel seems featureless, the magnets generate the pulses in the pulser coil at very precise and repeatable location. The flywheel magnets do have north and south poles, and are installed in the flywheel in a very carefully placed orientation with respect to the keyway. Honda figured out exactly where to place the pulse generator coil so that the pulse that triggers the CDI happens at exactly the right location. This configuration gives one spark per revolution of the crank. On a side note, there is an extra unnecessary spark at TDC on the exhaust stroke, wasted spark.