One for the electrical engineers.

ferball

ferball

New Member
I have recently become quite intrigued by the idea of an adjustable timing for our little HT two strokes. Most threads seem to focus on the key way and magneto, but I have an idea/question for somebody with more electrical knowledge than myself.

The ignition signal is part of the AC wave produced by the magneto. I even read that simply placing a resistor between the blue wire and CDI would retard timing. My thought was a simple adjustable "phase Shift" circuit inserted between the magneto ans CDI would allow us to manualy alter signal wave by calculable amount, thus allowing for adjustable timing. Is "Phase shifting" the right concept? Or is there some other/better way to delay the magneto output? because if you can retard timing enough the engine would think it had been advanced thus allowing for fully adjustable ignition timing.
 
You could use an RC network to create a phase shift. By using a potentiometer for R you can make it variable. To go a step further, you could have the pot controlled by the throttle for variable phase shift controlled by acceleration.
Another way is to use a long piece of coaxial cable to create a delay line, sort of what was used in some analog oscilloscopes.
 
That would be an interesting performace MOD, ten feet of coax wrapped around a seat post. I would have to actually get out my timing gun and measure crap to do it right, because my understanding is 4 degrees in one direction or the other should be more than enough "adjustment" to widen the power band a bit.
 
Now that I think about it, a coaxial delay line for the frequencies involved would be too long to be practical.
Probably the best bet is build your own CDI from schematics and vary the RC components in the SCR's gate circuit.
 
Here is a link with schematics and instructions on doing what you set out to do.

Radioshack some soldering skills and the ability to read the schematic is all that is required.

If you need help reading the schematics let me know.

If you cant solder buy breadboard.....its circut board that has pre drilled holes in a grid where you just snap the components in like leggos.

http://www.electronics.gompy.net/cdi/
 
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...that looks delicate and expensive. I'd be as interested in longevity as well as actual function.
 
If you wnat cheap and easy for around $50.00 you can find a dual curve switchable CDI.

The above method is real cheap prolly cost $10.00.

Personally i would just buy one then all you need is a hall sensor on the magneto.

My only intention was to post for you guys the information to try what you were talking about.
 
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