How to fit electronic ignition

Information relating to the Matchless G2 or AJS Model 14 250cc Lightweight
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How to fit electronic ignition

Postby clanger9 » Wed Jan 09, 2019 5:57 pm

OK, this isn't one for the purists, but I've had a go at writing a guide on how to convert a Lightweight to 12V and fit Boyer Bransden ignition:
https://www.ifixit.com/Guide/AJS-Matchl ... ion/117791

It's a bit work-in-progress (and the 12V stuff was done from memory), but hopefully useful for someone. Also, my bike isn't very standard in terms of wiring, so some of the photos might hinder rather than help. ;)

I also made a new wiring diagram for 12V. I think I got everything right, but it could do with a bit of checking.
https://d3nevzfk7ii3be.cloudfront.net/i ... LKueS.huge

If I've made any glaring errors, please shout here (or just log in to iFixit and make whatever changes you like, I'm not precious...)
1966 AJS Model 14 250 CSR "cafe racer"
1993 Ducati 750SS

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Re: How to fit electronic ignition

Postby ChrisTheChippy » Wed Jan 09, 2019 11:00 pm

Horay , thanks Clanger . I'm absolutely rubbish at wiring don't understand it at all but I'm going to have a go at converting to 12 v and this will definitely help . I do want to retain the original points system at this stage but will see how it goes . I won't be able to make a start for a couple of months but it's reassuring to know this resource will be there to refer to . Expect some daft questions :D .
Cheers Chris .

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Re: How to fit electronic ignition

Postby clanger9 » Thu Jan 10, 2019 7:48 am

Yay, you get to be the guinea pig then! :D

If you want to stick with points for now, here's the link to the 12V conversion only:
https://www.ifixit.com/Guide/AJS-Matchl ... ion/117790
1966 AJS Model 14 250 CSR "cafe racer"
1993 Ducati 750SS

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Re: How to fit electronic ignition

Postby ChrisTheChippy » Thu Jan 10, 2019 10:35 pm

Thanks Paul . In a weird way I'm kinda looking forward to doing it now . Let's hope I can meet my nemisis head on .
Like I say it will be started in a couple of months but I will let you know how I get on .
Cheers Chris

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Re: How to fit electronic ignition

Postby Martin.S » Fri Jan 11, 2019 10:47 am

Superb - Thank You Paul.
Watching the heat mark on the plug electrode is a new one on me - great advice.
I gather you ordered the parts direct from Boyer - so why the two coils on the stator plate? . If you were to of just wired one coil in would that not save a little power and also reserving one as a spare?
Thanks again

EDIT I see now that Boyer use two stator coils on all of their side point single models - Why?

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Re: How to fit electronic ignition

Postby clanger9 » Fri Jan 11, 2019 5:21 pm

Hi Martin - thanks!!

I originally got KIT00051 from Feked, because I'd read "somewhere on the Internet" it could be made to fit. It can't, because it has a 2.8" stator plate and a male rotor. I got in touch with Boyer and they said, not a problem, just send the rotor and stator back & we'll send you the right bits. I should have just ordered from them in the first place!

I'm not sure why the Boyer system has two pickup coils - I think it's a "universal" plate that has timing holes for both clockwise and anticlockwise rotation (that's what it says on the back of the pickup plate, anyway). On power consumption: it's noticeably lower with the Boyer. I think it just pulses the ignition coil as needed, unlike the points that have the coil energised most of the time. Drain on the battery when running seems to have fallen by at least an amp. My bike has a modern 12V 55/60W H4 halogen, which the alternator can't quite keep up with at idle. It usually shows a couple of amps battery drain when waiting at junction, though it goes positive as soon as I set off. I noticed on my test run that there was much less drain at idle with the headlight on, so that small saving is definitely welcome! An LED headlamp would solve the problem completely, but I've had two fail on me so it's back to the halogen for now...

The pickup coils are just wired in series, so it'll double the signal that you'd get from one coil. Maybe that helps make the triggering more reliable? Anyway it seems to work fine so I'm hoping to make it to the VMCC run to Rainford on Sunday (weather permitting!)
1966 AJS Model 14 250 CSR "cafe racer"
1993 Ducati 750SS

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Re: How to fit electronic ignition

Postby Martin.S » Tue Jan 22, 2019 2:11 pm

You can connect the three output wires straight into a three phase rectifier


Paul are you sure you use a 3 phase rectifier?

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Re: How to fit electronic ignition

Postby clanger9 » Tue Jan 22, 2019 3:14 pm

Yep. 3 phase connected across the 2-phase feed. The diodes sort it all out (it’s just using 4 of ‘em instead of all 6). There’s next to no cost difference, and impossible to wire wrongly...
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Re: How to fit electronic ignition

Postby dada » Wed Jan 23, 2019 9:07 am

Is it the only 12v system available ?

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Re: How to fit electronic ignition

Postby Groily » Wed Jan 23, 2019 9:52 am

There are several ways to skin this cat dada.

For a quick review, see http://www.norbsa02.freeuk.com/goffyalt ... wiring.htm

Options include using the alternator that's there with a pair of wires 'doubled up', or upgrading to a 2 wire stator, and using an A Reg 1 regulator & rectifier unit, Podtronics box or similar in replacement of the original simple rectifier. These are the options I've used a few times, using original, 120 or 200W replacement single phase alternators. The latter two are Lucas RM21 (120W) and RM27 (200W) ( not sure of Wipac equivalent). There is also the option to use a zener diode while retaining a simple bridge rectifier, but I like that less well personally and have converted bikes from the '60s with that early 12v option to run with A Reg 1s.

Three phase alternators, which require an 'A Reg 3' regulator/rectifier, are also available. They knock out c 175 W and are good at low engine speed.

For me, the advantage of a combined regulator/rectifier is much simplified wiring, and also the option to 'unuse' much of the spaghetti on the ac/dc type ignition/lighting switch on many machine.

You can 'do' a 12v ac harness with about a dozen wires at the most basic.

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