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Dominator 99 Electronic ignition


Just been think about fitting electronic ignition to the above. I realise this topic comes up regularly but looking for general guidance. Have fitted the above to my 1971 OiF Bonneville and it has been a revelation in terms of starting over many years. - normally first or second kick. Bike acquired in 2004. Just got machine out of garage tickled carbs and not started in 6-7 months but started on 5th kick and then after various rests from cold first time. So thinking about this for the 99 which I have had for 3 years. With the Triumph as many will know the essential bits are under the old points cover so bike looks standard but obviously the dommie has a distributor. How does the fitting of EI affect the look of the dominator. The Triumph also has 2 coils but my manual shows one only for the 99 so will I need 2?. With a magneto model like my 1957 Bullet I understand that the rotor element fits inside the cover and thus the bike again looks no different if EI fitted. While will get in touch with relevant parts suppliers not seen anything listed specifically for the distributor model 99 though some list parts for 'Norton twins'. The Triumph had a Boyer fitted in 2004 which was replaced with a Wassells in 2019. Both were/are effective so indifferent really given this experience. I realise that some may think this a very basic question but any advice appreciated. Hugh     


I have fitted a Boyer to my 1959 99 which has a distributor as standard.  You have to make a small modification to the dis cap (a half round scallop) and remove the mechanical auto advance retard unit, but it's quite an easy job and makes a big difference to performance and starting.  I use a dual coil.


Hi Hugh.

I have a dommie 99 fitted with  Boyers electronic ignition.  It was fitted by a PO and had a faux magneto.  From what you say I think you may be trying to use your existing distributor to control the spark timing, if you are these points maybe useful :

The distributor cap will be no more than a protective cover for the timing unit. (the circular plastic disc with two inductor coils on top and a rotor with magnets attached.)                                        Start by removing the two screw that hold the contact breaker plate in place and remove the plate.  Next, remove the screw from the cam and remove the cam.  This should, I hope, enable you to see the end of the distributor drive shaft.

Fit the rotor to the end of the shaft using the screw that held the cam in place with the magnets facing upwards. The disc should be fitted on top of this and fastened in place using the two screw from the breaker plate.  (Not too tight yet)

The two leads from the disc, which are colour coded,  must be connected to the matching leads on the amplifier.  One of the other leads on the amplifiers connects to the high voltage coil.

 On my bike (with a 12V battery) I use two 6V coils connected in series to drive the spark plugs but you could just as easy use a twin output coil.

The amplifier has 5 leads coming out of it, a negative supply lead, earth lead, two leads from the timing unit and one to the coils.  Mount the amplifier where it will be well ventilate to keep it cool.

Hope this helps.  Peter







How does the current Boyer  Advance curve compare to the early Boyers and the orriginal  lucas curve?. Does the Boyer box  now have a timing indicator light?. Is there still a problem with kickback at low voltages?  These  concerns were always an  issue for me. Should be solved by now.

Please excuse the personnel email but thank you Peter for your advice.. Very useful. At moment been struggling with what I think was a gummed up carb. Used something called mechanic in a bottle which has seemingly done job adn feul flows in more freely and starts quicker although still needs several kicks I will file this away and when warms up in garage have a go. By the way which system did you use? Thanks again. Hugh


Oops too early in morning. Boyer of course. Hugh.


I used the Electrex conversion which has a tiny CDI unit and double ended "lost-spark" coil both tucked up invisibly under the front of the tank.

The alternator output is only 50W, but there is no ignition loading of course (it's completely separate). Positive or negative earth. That's loads with led bulbs.

No points, no distributor, no large coils.




In reply to by steve_marshall1


Hi Steve.

I built a CDI unit many years ago for use on a car.  It worked very well. However, it made use of the distributor points to time it so that the plugs fired at the appropriate instance. (and the rotor to select the desired plug)   Does the Electrex  version have a different timing method?  Things must have moved on in the last 60 years!

The CDI system I am familiar with relies on a capacitor being charged to about 200V. When triggered, the capacitor discharges, via a thyristor, through the primary side of the coil.  The 200V is stepped up by transformer action to give a secondary winding voltage of about 20 to 30 KV, more than sufficient to fire the plugs.  This takes a very small current.  The Boyer, effectively, just replaces the mechanical points with electronic ones with little saving on current consumption.









I made several abortive attempts to  replace my dissy points with an EI   system  , just could not get it to run.  It has just occured to me that  I may have had a 2MC    capacitor  fitted !.  Seems a distinct possibilty that  it was not  compatible. ?. I do know that the early Boyer will work with one.


Starting at the above by Robert T, the presence of a 2MC (or modern equivalent) does NOT hinder the Boyer or any electronic ignition. Under normal battery, coil (electronic or otherwise) ignition the 2MC is nothing more than a micro battery. Under flat battery conditions it aids starting and reduces kick back. The traditional Boyer Mk 4 even Mk 3 and I believe all the digital units do not have any built in timing light as they rely on the ignition rotor moving to create a spark, no movement= no spark hence no 'static' timing light.

Going back to the original question re fitting a Boyer ignition to an 18D2 Domminator dizzy, I supply a kit that does not need the body of the 18D2 being cut about or the Dizzy cap. I can even supply an 18D1 cap to make the 18D2 not look like a 'cows udder'. I advocate 2 6V coils and the machine changed to 12V. Further information on


I am an electrical engineer but I know nothing of the inner workings of the Electrex. The timing is simply getting the angular relationship between the rotor and the stator correct. At a certain point of rotation it makes sparks! Obviously it is fully retarded when starting with (I suppose) a normal auto advance curve. 28 degrees for Nortons. The markings on the rotor & stator make static timing a no-brainer.

It has five wires, two go to the rectifier, three go to a 5cm x 5cm CDI unit, which has two short flying low voltage leads to a small lost-spark double-ended coil. I bolted both of them to the head steady, up out of sight. You could put them anywhere really.




The Electrex sounds interesting , it sounds (from Steve's comment)  that it may be possible to static time the ignition. The low output would not suit  my Norton but would be fine for another bike that needs a new alternator.  I have had  Mains strobes for 30 years  but have (up till now!) not managed to strobe the Atlas Boyer  which runs by guesswork..The Atlas would have  needed  3 people to strobe it (2 to hold it down). Now re-built with lightened and balanced pistons ,I may get round to trying again. Amongst the dozen or more family machines I get to work on there is  every concievable type of EI. And I still like points  combined with EI and built in  timing  light. The ability to fix by the roadside and make tiny adjustments to timing  with ease  still  holds me. I have old  memories of abandoning cars and bikes in far away places  and epic roadside  repairs ,   Solo no hoist Engine out clutch replacement  frogeye Healey, Diff strip ,same car, Re wiring burnt out electrics ford pop on the south circular , Filing 88 pistons on the M1. Replacing 18d2 dissy on Regent St . All seemed normal back then.


Before you rush out and buy anything from 'Electrex World ' please do a search for it on the forum. Within the last year, Grant Tiller  responded to a similar question with his findings and it makes alarming reading. Other members have had bad experiences too.

Fwiw, I fitted a  'mushroom' housing' and Boyer to my 650 over 20 years ago and have no regrets.

Remember-if something sounds too good to be true,  it probably is!

Regards, George. 


I have a Boyer on my 99; it replaced a K2f mag that was never far from being problematic.  It then started easy, ran a treat, with (in my mind) a much better advance than the mag ever had.  However, heed Al Osborn when he says make sure your alternator is 12v!

After fitting the EI, I found that my 99, although starting easy when fresh from the trickle charger, suffered from bad, actually wouldn’t start, after a run of 20 miles or so. After sitting for 15 mins, it would normally kick back, then eventually start.  I put this down to Ethanol, and did all I could to improve the carb to head insulation - but it still didn’t start very well after a run. 

To cut a long story short; the problem was that my alternator, although 12v, was still set up for alternator switching, (as per running with a mag).  The 2amp Boyer load appeared to be pulling the battery voltage down on a longer run. The battery recovering enough after some sitting time to start it again. Changing the alternator output to full (non switching) 12v, fixed the starting problem! 

So my advice is get all of the benefits of Electronic Ignition - BUT please make sure your electrical system is up to the job of maintaining a healthy voltage under all conditions...

In reply to by steve_marshall1


Hi Steve.

The Boyers does have a static timing facility, it consists of two holes adjacent to and in-line with the two inductor coils.  From memory, to time the ignition the following following steps should be followed:

a)     Make sure the advance/retard mechanism is locked permanently in full advanced position.            My bike has a plain sprocket  instead of the a/r sprocket normally found on the distributor                tapered input  shaft.  This makes life easier.

b)     Set the engine to fully advanced. e.g.  30 degrees before top dead centre.

c)     With the rotor slightly loose on the end of the shaft, rotate the rotor until the screw heads of            the magnets appear in the centres of the holes.

d)    Tricky bit.  Tighten the rotor on the shaft without anything moving out of position.                             Small errors  can be corrected by loosening the two screws holding the plastic (or what ever           material it is made of) disc and rotating it a few degrees until the screws appear in the                    centres of the holes. re-tighten the two screws.  You could, alternatively, have the rotor fixed on the shaft to start with and locked in position and use the sprocket (loose) on the end of the tapered shaft to set the timing, then tighten the sprocket on the shaft with nothing moving out of position. It does mean you have to have the timing cover off to expose the timing chain.    Easier said than done!   

This should be enough to get the engine running.  You are recommended to use a timing light to get a more accurate result.

 Hope I haven't made a pigs ear of this.    Peter  


Several points here are wrong. The Boyer Mk3 and MK4 do NOT have timing indicator light. Alignment through hole etc is to get a starting point.

You do NOT fix the auto/adv/retard in any position if you are fitting Electronic (BBMK3/4) as the adv/retd is built in.

There is mention here of a sprocket lose on the TAPERED shaft. Tapered shafts are for magnetos. and maybe magneto replacement kits (Mushrooms) the sprocket must be a manual advance type with these and not needed to set the timing, you do that with the Boyer Brandesdon rotor as mentioned above.

Also mentioned above is an a/r sprocket found on a distributor-NO. the Distributor (18D2) has a plain shaft no way of altering the ignition timing as the sprocket is pinned on. The a/r mechanism is inside the distributor, and needs to be removed if fitting full electronic ignition.

Onk onk

In reply to by george_farenden


Hi George - Electrex

I would be interested to read more. I did a search and I didn't find much negative stuff about the Electrex, except for the puny 50W output.

The Grant Tiller link is "Error 404 Page Not Found" What did it say?

Electrex recommend running your lights (and horn?) directly on ac, but Paul Goff's led lamps are not all ac compatible, and I don't know what would happen to an Altette if it is fed ac.

The way to go is all led lamps, rectifier, small lead battery and possibly a tiny modern horn - if you use it a lot.

Electrex + 35W tungsten headlight bulb, not a practical option.


I left my auto advance in place when I fitted electronic ignition. Took out the springs and put them for safe keeping in my Dommie box. Wedged the auto advance on full advance to set the ignition. Took out the wedge. It goes immediately to full advance when it spins on the kick start, and that works fine and has done for 15+ years. 


Grant Tillers notes are here:

As you have said, 50W is moped sized output. Unknown is at what revs it delivers that. My Morini with direct ignition and 100W alternator balances a 35W headlamp, 5W tail lamp at 3500rpm. 

Maybe enough for daytime running with lamps on, but I imagine a moped style glow worm at idle/round town running? As for after dark, unlit road running...


Thanks George

I read Grant Tiller's very honest review with interest, but I have to report the diametrically opposite experience really.

I also fitted it along with a belt drive and I expected a fair amount of fettling. I think that it might be a very easy installation with a simplex engine sprocket, but I haven't verified that.

I needed custom spacers, machined down retapped Commando mainshaft nut etc. Tony Hayward was also very helpful to me. 

I have the distributor still in place to look right, but no internal chain to drive it. It leaks oil!

I got good support from Electrex when I managed to lose my coil bracket (it isn't on their official  list of parts - they just put one in the post for me gratis).

I asked them a couple of technical questions too, and got prompt, competent answers. Using it with a 35W tungsten headlight lamp is a non-starter (pun intended) although it will start OK of course.

Paul Goff quotes 1.4W for his led taillight and 7W for his headlight, so the 50W limit is not really an issue. You do need the rectifier/regulator though, Mr Goff's headlights don't work on ac. Probably a small lead acid battery also. Mr Goff says the headlight should be OK with rectified, unsmoothed ac, but no guarantee.

A fully charged 6Ah battery would keep the lights on for 8 hours, with no alternator at all.

Starting for me is fine too. It just has to be more reliable than a '61 Lucas points/bobweights/coil/distributor/alternator setup.

Lastly you need a 1-0-1 Ammeter instead of 8-0-8. (-;

Hi Alan.

I did make some mistakes in my thread and I was about to apologise for writing it before going into my unheated garage to do some research.  However, I never said anything about an indicator lamp.  It was mentioned, by someone else, in an earlier thread!

My first mistake was to suggest there were two holes in the disc, there is in fact only one and it is positioned to the side of one of the inductor coils.  You still align the screw head on the rotor so that it is in the centre of the hole.   Obviously, it is at this point where the magnetic flux of the rotor magnets begins to rapidly build up in the coil cores inducing the rising leading edge of the voltage waveform of the pulse.  The switching amplifier is triggered by this leading edge and cuts of the current to the ignition coils for a short period. 

My second mistake was to assume, wrongly as it turns out, that the mechanical configuration of the distributor drive input would be similar to that of a magneto system.  I did mention in an earlier thread that my distributor experience was limited to cars.  My bike, although a 99 deluxe, came with a mushroom style electronic magneto.  I should have realised that the distributor advanced was controlled by bob weights and springs, like a car.  

Mia Colpa.    Peter.


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