Electronic ignition conversion

[Mikep]

Hi everyone,

I currently have a 1973 Honda CB125 S which obviously has conventional ignition timing. I think the cam on the advance unit is a little worn therefore not opening the points as efficiently and rather than buying a new one is there a kit availbale to convert this bike to electronic ignition as this would be one less thing to maintain and would make the bike that bit more reliable?

Any help is appreciated.

Mike

[Robby]

Newtronic should do a kit for it, but for the price and hassle of fitting electronic ignition you might as well fix what you have.

[Blau Zedong]

I don't think Newtronics (or Autocar or whoever holds the rights to them this week, I still call them Pirahna!) do one for the CB, most of their systems are for bikes with active ignitions (battery and coil) and I'm sure the CB uses a magneto to power the points, which wouldn't work with the optical sensors used on Newtronics kits. You shouldn't have any probs if you fit a new (or better condition) points can and use OEM points and condensor.
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18:54:59 Rob Fzs: unless its their clothes/ hair/ golden teeth

[Mikep]

The reason for thinking of changing is because I think the advance and retard unit may not be working correctly and this isnt a cheap part.
I took the bike out yesterday and it did not want to rev beyond 6000 rpm and it seemed just like in a car when it hits the rev limiter. I can only assume that the spark isnt being advanced correctly. The bike has had a total restoration and although its had new points, condensor and spark plug I haven't been able to get it running properly since.
I did remove unit today and found that the seemed to be ok and the springs worked and it snapped back as it should, but would the cam on the end that operates the points have anything to do with this problem if its worn?

[Teflon-Mike]

The CB125S single, is the same bottom end as the CB125RS, and the XL125, engines, as far as I'm aware....

We then delve into the realms of 'Small Honda' parts interchangeability and compatability.....

AND.... I would start by trying to get hold of a rotor and back-plate, and possibly the magneto cover from, a CB125RS, XL125 or possibly later CDi ignition CG... or better still, cheapo-chinese-fake-away clone....

Not only CDi ignition but 12v generator..... full 12v conversion.

I would want the CDi unit from a CB125 Super-Dream, as that is the most 'peppy' and doesn't have inbuilt rev limiter.

A 12v regulator, to 'match' source stator, and 12v battery....

Full set of 12v bulbs and you are away..... wiring, rated for amps, power = volts times amps, so double voltage, halve amps, wiring & switches will be well up to it. Oh... you'll want a 12v indicator flasher....

The Small Honda CDi ignition does away with points & uses 'pulsar' induction trigger in the crank-case, you'd need to make sure you got that, either on the stator, or in the mag-casing.

Remove points & advance mechanism, and blank off; and you ought to be 'set'...

Might take a bit of head scratching and muggering about, but that's where I would start my investigations.

You may be able to source proprietry aftermarket CDi ignition; Barwell, do custom made for old trials bikes; then there's Boyer Brandsen. These are FAR from cheap though, you are looking at a couple of hundred quid up.

The cheap 'electronic' ignitions, like the Piranah, or the Maplin generic, are not strictly CDi ignitions; they are often contactorless amplified ignitions.

Opto sensor and amplifier replace the points, to fire the coil, they have no in-built advance/retard system, they rely still on the mechanical advance mechanism.. they simply do away with the points!

That's the 'beuty' of the Small Honda CDi, it has an 'advance by retard' mechanism in it... timing is set to maximum advance, but CDi counts clicks, to deturmin engine rpm, and from trigger signal, counts a delay before firing coil.... 'retarding' ignition, at lower revs.

Ie does job of points, and advance mechanism, which is the bit that is bothering you.
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Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'

[temeluchus]

quick google found this:

https://www.cb450ignition.com/CB125S.htm

***EDIT****

Retains the stock advance so may not be much use, dangit!
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Some shite cruiser. Now with guns and FREEDOM!

[temeluchus]

https://www.elektronik-sachse.de/ZDG3/HONDA/CB175/zdg_cb175_en.htm
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Some shite cruiser. Now with guns and FREEDOM!

[Fizzer Thou]

I used to have a 1972 CB125s.It used points,a condenser,a mechanical advance/retard unit and needed the battery to power the coil standing voltage.When it was working correctly,which was the majority of the time,it gave faultless performance.

Until one day the teflon heel which is worked by the cam of the advance/retard unit wore.I regapped the points to the correct spec but it just did not work as before.Once I replaced the points and gapped accordingly it was fine once again.

Have you had the auto advance/retard unit apart?Did you make a note of which way the cam goes back on,as it is possible to reassemble it 180 degrees out.From what I can remember,there are two dot punch marks which must be aligned for the unit to work properly.

Have you tried a new plug cap?I remember having awful problems with the OEM metal cap back in the mid-70s.Then NGK brought out the plastic caps,which immediately solved several running problems,like the engine cutting out when running in heavy rain when using the indicators.Even if the plug cap looks okay,I have seen these in such bad condition where a small crack in the plastic has been enough to lose the high voltage from the coil to earth.This shows up well in a dark environment - nice blue sparks.

Boyer-Bransden used to make a points assisted ignition pack.This removed the arcing across the points that occurred.In fact I still have some,but they are meant for a 12vdc system.These packs still use the mechanical advance/retard unit though.In the past I have used a full Boyer-Bransden system,which replaced the points back plate and the auto advance/retard system.This utilised a laminate back plate with two Hall effect transformers which had a voltage induced into them from a magnet mounted onto the end of the crankshaft.This low voltage signal was then sent to an amplifier pack,which performed the electronic advance/retard,and,using the bikes 12vdc supply,triggered the switched signal to the coils.It was very reliable and only died when the bike was destroyed in a fire caused by a head-on with a car.
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Just talk bikes.What else is there?

Always have a 'Plan B'

[temeluchus]

[Mikep]

[Fizzer Thou]

The comment that you made about a garage sorting the carb may well be pointing to the problem.From what I remember the float was a metal one which was soldered.If this is not shutting off the fuel flow correctly it could be allowing too high a float height,causing the engine to run rich.

Please excuse the braincell depletion,but it has been a few years (35) since looking into the depths of a CB125S engine.I can recollect a float valve without a rubber tip,it being a plain metal taper that seats into the valve seat.

I also seem to remember a gasket being either side of the inlet manifold spacer.If there is nothing there,you could try using some Blue Hylomar,thinly smeared onto each face so as to stop any air from being sucked into the engine and causing a weak mixture.This could explain having to run the engine on choke,so trying to compensate for the weak mixture.
As a quick test,run the engine and spray some Easi-Start or WD40 around the inlet manifold.If the engine picks up and starts to rev,then there is the problem.
____________________
Just talk bikes.What else is there?

Always have a 'Plan B'

[Mikep]

[humanbeing]

There's some weird "chinese" solution IF u're skilled
https://www.bikechatforums.com/viewtopic.php?t=225356