Fit­ting a Boyer to a Dom­mie twin

Classic Bike (UK) - - Contents - WORDS & PHO­TOG­RA­PHY: RU­PERT PAUL

Fit­ting elec­tronic ig­ni­tion to old Brit bikes is usu­ally straight­for­ward, and Boyer’s is prob­a­bly the most pop­u­lar sys­tem. They cover a good range of bikes, their web­site has de­tailed, model-spe­cific info, and you can speak to some­one in­tel­li­gent if you hit a snag.

The ba­sic idea with a Boyer is to un­screw the points and me­chan­i­cal ad­vance/re­tard, and screw in a ro­tat­ing mag­net, fol­lowed by a plate with a coil or two. As the mag­net spins past the coil, it gen­er­ates an elec­tri­cal pulse which goes to the ig­ni­tion box. The box am­pli­fies the pulse into a spark, and oblig­ingly pro­vides an ad­vance curve to re­place the func­tion of the orig­i­nal bob­weights.

Once you’ve en­sured that the spark hap­pens at the right mo­ment (you’ll need a strobe light), you tighten ev­ery­thing up and en­joy ex­cel­lent start­ing and per­ma­nently ac­cu­rate ig­ni­tion tim­ing. Which is fine – un­til you dis­cover there isn’t a kit for your bike, such as this sin­gle-carb Nor­ton Dom­i­na­tor in a Featherbed frame. I was mak­ing a new loom for it and the owner, Jono, wanted to take the op­por­tu­nity to con­vert to elec­tronic ig­ni­tion.

A call to Boyer re­vealed they don’t do a kit for this model (nor does any­one else!), and sug­gested

I call Alan Os­born at long-es­tab­lished AO Ser­vices in Nor­folk (01953 884681). Alan uses Boyer com­po­nents to make a ro­tor and coil that fit in­side the orig­i­nal 18D2 dis­trib­u­tor hous­ing, plus a sin­gle-cylin­der am­pli­fier box with two 6V coils. The kit costs £165 in­clud­ing P&P, plus an £18 op­tional alu­minium cap to tidy up the dis­trib­u­tor.

Elec­tri­cally, it’s as sim­ple as any other Boyer. Two wires take the tim­ing pulse from the source coil to the box. Three wires go from the box to the rest of the bike. One of them is live when you turn the ig­ni­tion on (and also con­nects to the coil live ter­mi­nal), one is earth and the third sends the sig­nal to the coil. It works per­fectly, but when you’re deal­ing with a 55-year-old cafe racer there are a few other snags to over­come. Turn over to find out how to deal with it.


Elec­tronic ig­ni­tion kits aren’t avail­able for some clas­sics, like this Dom­mieengined spe­cial, but we know a way around it...

Make a neat job like this and save your­self a lot of kick­ing – it’s not dif­fi­cult

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