Ignition Toni twins

Two issues on my bike, 1/ intermittent faulty ignition switch 2/ poor quality spark
First bypassed switch as a temporary measure, switch under seat. Fine until I left it on promptly cooked the battery.
Second measured spark on flash test I know crude but wouldn’t make the green zone at all. Primary circuit fine low resistance. Note Falcone mag well into green zone ( old technology? ) Replaced with coils from Flee bay which are also wrong diameter think £18 each. No difference. Managed to fit Lucas sport coils much larger in side panel they are also 3 ohms resistance now have lightening :grin:
Does anyone know the real reason and maths for fitting a balance resistor as in classic cars and Norton’s. The theory is that this greatly improves starting when the amps are drawn to the starter especially in winter ? Mk2A have 6 volt coils, resistor and the “blue thing “ a large capacitor you could start with a flat battery a bloody good idea. Looking at circuit if one set of points is open then 12Volt /3ohms = 4 amps ? If both points are closed think they must be at some point, then 1/R+1/R (parallel circuit) equals 12/.66 a lot both more than expected. Would the Commando ignition be an improvement? Tending to steer away from fully electronic it’s great til it fails, could carry mounted on bike two spare coils. The bit I do t get, the resistor impedes the “flow” I assume why does this reduction help particularly with 12Volt coils ?
Regards Ratt

A “ballast” resistor is used to help starting. The coils used with ballast resistors are rated at a lower voltage than the vehicle, and the current through them is limited by the ballast resistor when running.

When starting, the starter relay shorts out the ballast resistor, and applies battery voltage to the coils, it’s only for a short time so they don’t burn out.

This is particularly useful when the battery is a bit old & sad, as there will always be a voltage drop when the starter motor is drawing current (lots of current…), and the ballast system counteracts this.

They’re not much help if you have a kick-start…


Thanks Simon,
So on electric start the period you push the button and starter engages the ballast resistor is not in the circuit and higher than expected voltage/current passes through the coils? When the bike starts then the resistor returns to the circuit and voltage/ current is reduced to prevent failure?
On a MK2A Norton only kick start I assume the output of the alternator must be used/measured to switch the resistor…

Thanks regards Ratt

Sorry, I have no idea how a ballast resistor is used in a kick-start vehicle.


Were the 6v coils in series perhaps, i used to run a Triumph on a wasted spark setup. If remember rightly some trials bikes were run without a battery and used only a capacitor. I ran one of my bikes just on a capacitor for a while and had one which would start without battery or capacitor, the alernator providing the power for the spark, timing was critical. I think Triumph called it an “Energy Transfer System”.

A ballast resistor is only used in cars (and I don’t know of any that do) which have an electric starter, for the reason already described. Not applicable to motorcycles (and especially if kickstart). There must be another reason for your weak spark problem, a ballast resistor won’t fix it. :smiley:

Thanks all, well back in the mists of time I seem to remember my Norton MK2A ( the best) have both “ the blue thing” and a ballast resistor. The MK 3 had electric start. Will have a look again.
I don’t have a poor spark now as two Lucas sport coils, if you have an ignition problem be wary of the coils on Flee bay for the bike they did not fit
And we’re no better than the originals.
For you single guys my test rig I constructed for the mag using a battery drill produced a spark of 18mm which I thought was real good as the magical little box suddenly produced this simply by spinning it around :grin: Didn’t open up to this size for long as you can shortout the secondary coil the size of which is amazingly small.

Xmas greetings Ratt