Hi I was searching for timing tips for my 1983 230E when I came across your thread.

In analog circuits zener diodes are often used to provide a fixed reference voltage (zener diodes are available in many set voltages). This essentially accomplishes the same thing as a resistor (increasing your resistance lowers your reference voltage.) A zener diode is superior as the output will remain steady even with slight input variation thus providing a more stable reference voltage. You could adjust your timing by substituting a different voltage zener.

Hope this helps.

...Nicholas

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Almost mint 1983 230E eurospec.
Honda civic for those not so mint moments.