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Helping keep British Motorcycles on the road for over 30 years - established 1977



The Boyer-Bransden MK4 is a contactless ignition system utilising an advanced and patented trigger switching system and featuring electronic advance and retard. The kit replaces the auto advance unit, points, points plate and condensers. Engines function best with a retarded spark for starting and low revs, but need ignition advance to run at high speed. The MK4's analogue system simply advances the spark at a set rate from fully retarded to maximum advance, as engine speed rises from zero to 4,000 revs. Thus eliminating the inaccuracy of mechanical advance/retard units. The Boyer-Bransden Mark 4 Contactless Transistor Ignition provides absolutely accurate timing for motorcycles. Once set it cannot vary its precision. It incorporates an advance and retard circuit which has no moving parts and is fully sealed for life in a material which is water, petrol and oil proof. It simply cannot wear out. There are no "rubbing parts" - no friction. There is a much better spark - at all engine r.p.m. figures. For improved economy, starting, smooth running, and all round performance, you can't beat the MK4! See the 331-Series in the Price Guide for price and availability. Replacement parts are also available. Warrantied!

NOTES: Coil Requirements - Boyer Electronic Ignition Kits work best with less than six ohms total resistance on the primary side of the coils. Since the coils are wired in series, the resistance is the total of all the resistance in all the ignition coils in the system. Stock 12 Volt coils have 3.5 ohms of resistance each, so a twin cylinder bike with two coils has a total resistance of seven ohms, and a three cylinder bike has a total resistance of 10.5 ohms; both more then the limit of the Boyer kits. The modification is to install 6 Volt ignition coils, which have a resistance of approximately 1.7 ohms each, so that the total resistance in a twin is 3.4 ohms, and in a triple is 5.1 ohms, both within the allowed impedence range. Only the the ignition system is involved, nothing else needs to be changed. Since single cylinder bikes have one coil (3.5 ohms) they do not require a new coil. Later Norton Commandos have six volt coils with a ballast resistor so the coils are kept and the ballast resistor removed. Every kit is supplied with complete instructions and a troubleshooting guide.

Ignition Box combines the Boyer Amplifier with the Power Box that
replaces the rectifier, zener diode and capacitor.
(For no lights operation only)

For instructions please see the Tech Help Page

331 Series - Boyer Electronic Ignitions

Part Number        Description


331-01      Boyer elec.ign, Norton

331-01/B    Boyer MicroPower kit, Norton
331-02      Boyer ign, TriBSA unitTwin
331-02/B    Boyer MicroPower kit, TriBSA unitTwin
331-02/C    Boyer race Ign/reg kit, Com & TriBSA unitTwin
331-03      Boyer ign, TriBSA Triples
331-03/B    Boyer Micro Powerkit, TriBSA 3
331-03/C    Boyer race Ign/reg.kit, TriBSA 3cyl.
331-04      amplifier, Boyer, Commando
331-04/B    amp, Boyer, Commando Micro Power  
331-05      amp, Boyer, 2cyl. TriBSA
331-05/B    amp, Boyer, 2cyl. TriBSA, MicroPower  
331-06      pickup plate, Boyer, 1&2 cyl
331-07      rotor, Boyer, 2 cyl, late 1cyl.  
331-08      pickup plate, Boyer, 3 cyl.
331-09      amplifier, Boyer, 3 cylinder  
331-09/B    amp, Boyer, 3cyl MicroPower  
331-10      rotor, Boyer, 3 cylinder  
331-12      Boyer kit, TriBsa single, 64on
331-12/B    Boyer Micropowerkit, unit 1cyl, sidepoints
331-12/C    Boyer race ign/reg, unit 1cyl, sidepoints
331-13/B    Boyer MicroPowerkit, unitDist. 1cyl
331-13/C    Boyer race ign/reg, unit 1cyl, distr.
331-13E     Boyer kit, TriBsa single, distr.
331-14      Boyer elec. ign, Bullet  
331-14/B    Boyer MicroPowerkit, Enfield Bullet
331-15      Boyer ign, TriBSA unitTwin, 6V
331-16      amplifier, Boyer, 1&2 cyl, 6V  
331-17      coil, single output, for Micropower only 33117.jpg (13310 bytes)
331-18      coil, dual output, for Micropower kit

33118.jpg (17441 bytes)

331-18/A    coil, dual, Boyer 33118A001.jpg (12018 bytes)
331-18/B    heatsink, for coil 331-18/A
331-19      amp, Boyer, TriBSA unit 1cyl. MicroPower  
331-19/A    amp, Boyer, TriBSA unit 1cyl  
331-20      ignition/powerbox, racing  
BCS Part #331-30 Boyer Micropower K2F Magneto Conversion Kit
SRM-MAGKIT-1 Click here for instructions (pdf)
BCS Part #331-35 Boyer Micropower Magdyno Conversion Kit 
SRM-MAGKIT-2 Click here for instructions (pdf)
331-50      electronic ign, singles & twins, SPARX