electrical

... but I think you may be confused between ignition and charging. The Zener has nothing to do with the ignition system - at least not directly.

Boyer instructions are available from their website but they generally recommend 6 volt coils wired in series giving a wasted spark system ie both plugs fire every top dead centre.

Re charging - you can have either a solid state rectifier plus zener diode or fit a solid state regulator. I'm happy with the rectifier / zener setup although it is inefficient in the sense that excess voltage is just dumped to earth and comes out as heat.

Don't want to divert the discussion, but the modern reg/rec boxes also regulate voltage by shunting ("wasting") current.

There are expensive and bulky exceptions, but who wants expensive bulk!

... you need the Boyer rotor, PCB and black box with connecting wires as well as 2 coils wired in series and of course HT leads, plug caps and plugs. Have a look at the Boyer site which has all the fitting instructions you need.

http://www.boyerbransden.com/instructions.html

... if you are using a simple rectifier (which is what I understand you to be saying) you need the Zener diode to regulate the voltage. If you're talking about the big blue capacitor you don't need that.

... I said that.....

Ah yes- I misattributed "that!"

Yes the Zener diode will dump power say it dumps 3A at 14V ie 42W is lost. 1 HP =750W so we are loosing 1- 17th of a HP!
Yes the reg/rect loads the alternator but I have not measured how much but I expect it will be more.
And another thing, the system will work without the Blue 2MC capacitor BUT it is recommended that you install one, it will help when trying to start with a flat battery and it reduces the ripple created by the reg/rect.

Someone has to stick the Zener diode and rectifier of a revving bike in an insulated vessel of water, of known mass, to see if the temperature rise is commensurate with 42 watts.

Michael-Electricity is much simpler than that Facts-
The Zener diode was designed to sunk 100w at what every voltage it is made for, in our case 14.4 (ish)Volts 14.4 at 100W is 7Amps if you push your luck over this AND without a significant heat sink, then BOSCH the Zener fails. So I have assumed you are only using up to 3Amps. NOTE-the RM21 'might' give 100W at 7K revs but on our tired Alternators/engines you might get 80/90W but then 20W is used by the ignition, and maybe another 20W to charge the battery, so you MIGHT have 3X14.4 =42W (with a following wind). So the amount of POWER lost in the Zener is not of significant issue.
By the way if you are worried about using 42W lost in the Zener diode , do NOT go out at night as putting your lights on will use another 55W!!!

The voltage drop across the Zener may not be a continuous 14.4 V and the alternator current output may be affected by reactance.

It's noticeable that my modern reg/rec, probably Mosfet, shunts 12 A alternator current but doesn't get hot.

If you have a working rectifier and Zener diode use them, but measure the voltage across the battery terminals at 4,000 rpm, lights on and off.

Use two 6 volt coils or one 12 volt dual HT coil.

Good advise Michael but I can check Zeners correctly if needed. All it will cost you is return postage.

Denis, is that a Trident condenser pack ,in with your electrics?

Yes that is a Condenser pack that can be used Trident. twin or even single (you would use just one condenser) But this bike has Boyer ( or any electronic ignition) Does NOT need condensers-they are for points ignition. Also the Blue 2MC is recommended, but this one being 60 years well passed its best so it is best to replace it.
Dennis you do NOT have a rectifier and Zener diode AND a regulator/rectifier. One system or the other.

... that capacitor and condenser are actually different names for the same thing - the former being the more "formal" term. For some reason the small one in the ignition system is usually called a condenser, the large blue one a capacitor. All calculated to confuse the innocent Norton rider.