Camchain and tensioner seen up close in a cutaway bike engine


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Ian Soady¹ said :-
In desperation I've ordered a pitbike (what is that?) complete CDI set from ebay. At under 11 quid it won't break the bank and I can start by fitting the coil.

I do appreciate I'm boldly going where no sane person has ever been before but I'm starting to think I've lost the plot. This theory has been compounded as I fitted a new back tyre to the Tri_Greeves a week ago and it's been losing air. Off with it to check the tube in a bath of water and nothing - until Electra suggested blowing it up a bit more whena small stream of bubbles appeared. The nip (yes I confess I did it) closed up when the pressure dropped. Rather than fart about with patches I'll buy a new one and hang the expense.

27/08/2023 16:45:17 UTC
Upt'North ¹ said :-
"In desperation I've ordered a pitbike".........I thought you had lost the plot!

27/08/2023 18:27:33 UTC
nab301 said :-
Ian , we've all been there with tubed tyres at some stage! Like Upt , my first thoughts on " I've bought a pit bike " ( before I read further) were, how is he going to fit on one of them!
Sometimes you just have to put the tools down and step away from the bike. Recently I received a freebie of a quite new non running Honda engined lawnmower , OHC wet (timing) belt design no less!
I didn't try starting it but checked for sparks and it appeared dead. Removed the coil , cleaned off the inevitable rust , refitted , still no spark , checked the resistance etc and it appeared to be duff , couldn't find a cheap coil locally , rechecked the original and it appeared to be ok....refitted and rechecked it numerous times , stepped away for a few days , regapped the coil carefully , this time i was in a dark shed... there was a visible spark , Oh dear . It started first pull . Cleaned the carb just to be sure and cut the grass...


28/08/2023 13:40:37 UTC
Ian Soady¹ said :-
I've now had a response from Carmo, the people who supplied the CDI, with some information they kindly omitted to supply with it. This regards wiring in a slightly different way to standard -including swapping 2 leads. I quote: "When the Carmo unit is not working as it should (small chance) than please swap the two wires as on the picture below". And guess what - when I did that I'm getting a spark! I have to say that I would have expeted them to know which way round the wires should have been connected.....

I'll throw the tank on tomorrow and see if it will actually start & run.
Posted Image

28/08/2023 17:08:04 UTC
Glyn said :-
That's great news Ian. When my brother gets in trouble with anything he puts it to the back of his garage, covers it up and comes back to it at a later date. I can't do that, I just have to keep going. I'm tempted by a Suzuki SG550 at the moment, a mechanic ( no really) has made a hash of getting the studs out of the head and broken fins in his unsuccessful attempt. I should just walk away but, I'm tempted.

28/08/2023 21:01:15 UTC
Ren - The Ed¹ said :-
Good heavens! There's some technical stuff going on here.

Yes, the notion of Ian Soady on a pitbike is hilarious. It's good to know that aftermarket CDIs are a thing and very affordable. Why you have to swap the wire over is a mystery though. I wonder if anyone does aftermarket engine management computers? I've seen people use a Raspberry Pi as a replacement but it's a complex drawn out affair for sure.

29/08/2023 08:26:41 UTC
Ian Soady¹ said :-
And... it runs! Sounds healthy as well but a road test will have to wait. The Cheap ebay one (less than £11) also arrived this morning so I thought I'd try that. Guess what - seems just as good. I could have saved myself £100 as well as lots of hassle.

For some reason the XBR CDI is a bit weird as it gets a 12V DC signal when cranking. The pin it uses for that is actually an earth on the replacement...... I have a feeling that feed may be there to retard the ignision so it doesn't backfire and cause sprag clutch issues.

29/08/2023 12:05:41 UTC
Ian Soady¹ said :-
I've just sent this to Carmo, the CDI supplier. I don't expect much of a response.

"Dear Robert.

I have now successfully got the bike up and running again althoughI have yet to road test it.

I have to say I’ve been disappointed with my experience with your company. First of all, the unit arrived with no instructions whatever and was described as “plug and play” on your website. It was far from this. When connected via the small harness you supplied I had no spark. This turned out to be because pins 1 and 4 were swapped in the link harness. I did try connecting without the harness and this immediately blew a fuse on the bike when I operated the starter – I now realise bacause the XBR CDI has a +12 feed on pin 5 which you have broken in the link harness. When I cut this wire and instead fed a direct earth to the CDI, connecting without the link harness, I had success.

I understand that this positive feed may have a function in retarding the ignition when the starter is operated, however cannot find any documentation to this effect. I would have hoped that you would incorporate this feature, or at least point out to the user that it existed.

I have in no way been helped by you other than your providing a link to an information sheet which you should have given me at the outset. You should also have provided details of the advance curve and other characteristics. I have spent hours in my garage checking other components (entirely unnecessarily) but have been greatly helped by members of an online forum who have made many helpful suggestions. I should not have needed to do any of this. The only positive aspect is that I have now learned a great deal about CDI systems.

It has become plain to me that the unit which you sell as specific to the XBR500 is instead a generic unit. This raises questions in my mind as to what the advance curve is and whether this has been tailored to the motorcycle or – as I suspect – you have merely used a standard curve which may or may not suit the engine characteristics. I cannot believe that you have actually supplied one of these units to an XBR500 owner and that they have fitted it without problems.

It may interest you to know that in desperaion I bought a generic “pit bike” CDI unit complete with coil from ebay at a cost of less than £12. This was delivered to me today and I find that it replaces your unit directly and seems to give similar performance. It’s interesting that the pinouts on this unit are identical to those on your unit WITHOUT the link harness ie with B/W to pin 1 and red/black to pin 6. I accept that its internal components may be inferior but am left with the feeling that I could have saved myself £100 or so by purchasing this in the first place.

I welcome your observations."

29/08/2023 14:37:28 UTC
Glyn said :-
Good interrogation Ian, hopefully you'll post their reply or at least a summary of it. It's pretty expensive but it would be great to get the bike ( with both CDI's) on a Dyno to see how similar they are.

29/08/2023 17:32:44 UTC
Ian Soady¹ said :-
I got more or less the reply I expected....

"Hello Ian,

I am sorry about all the trouble!
We try to update the website as much as possible, the information I gave you is on our website, see THIS LINK.
Any suggestions are welcome of course!

I do not advice to use a cheap (Chinese) CDI units."

No, you wouldn't given the profits you must be making.....

30/08/2023 14:55:37 UTC
Ren - The Ed¹ said :-
Yep, more or less what I'd have expected too Ian.

Now someone somewhere mentioned advance on CDIs. Do CDIs have advance? It is my (albeit limited) understanding that CDIs are incredibly simple things. The coils in the stator charge the Capacitor, then a trigger (typically on the alternator rotor) triggers the charged capacitor to discharge into the coils hence the spark.

31/08/2023 18:26:47 UTC
Ian Soady¹ said :-
Yes they do have advance as the signal that triggers them has no advance mechanism (at least on the ones I'm familiar with). I don't know how it works but suspect that it is a retarding function rather than advancing as how can it advance before it gets the signal? I believe that some devices work on the time difference between the positive and negative pulse. They are pretty complicated beasts inside I understand and my knowledge of electronics is far too limited to know.

There are essentially 2 main types: AC where the unit receives AC powwer from the alternator and internally rectifies it (like my XBR) and DC where it's powered by the battery (like the Boyer Bransden units beloved (or not) of Norton Commando and Triumph twin riders).

The diagrams below may inform......
Posted Image

01/09/2023 10:15:08 UTC
Ian Soady¹ said :-
Oh, Carmo, the supplier has now told me never to order from them again. I will have no difficulty complying.

01/09/2023 11:12:26 UTC
Upt'North ¹ said :-

01/09/2023 18:27:56 UTC
Ren - The Ed¹ said :-
Ooooooft! Yes how rude. One has to assume one of 2 things - either they have sufficient business to not worry about upsetting customers - or they're on the way to closing and don't care about upsetting customers.

02/09/2023 10:29:45 UTC
Glyn said :-
And that's the way our little group works, they'll never get any of my money and will never understand why they go out of business in the end. They probably just buy in and sell out without ever understanding the product very well. It's this brave new world apparently that relies on the Ponzi scheme stipulating that there's an endless supply of punters. In my day, the hardest thing to get was the customers so you had to treat them well. Advertising is easy nationwide or even global now so access to the buyers is far easier and cheaper... Remember the days of Yellow pages?

02/09/2023 18:14:23 UTC
Ren - The Ed¹ said :-
So CDI. If the pickup is set to say MAX advance, say 40 degrees BTDC, the CDI receives the trigger pulse at 40 degrees BTDC. Now without the use of a microchip the circuitry has to delay the spark, to say 7 degrees at idle. I'm certainly no electronics expert but the only logical way to "read" the revs without a microchip would be the current/voltage from the coils. Low current/voltage = tickover, high current/voltage = high revs.

The capacitor is only allowed to discharge and cause the spark at a certain level of "fullness". Low current/voltage charges the capacitor slowly, takes longer to reach a certain value. High current/voltage charges the capacitor quicker. Hence the slower revs creates less charge which creates more retardation.

I'm sure a real electronics expert will be able to explain how I'm wrong.

04/09/2023 08:06:30 UTC
Ian Soady¹ said :-
I think there are at least 3 ways to detect engine speed:

1. Measure the peak voltage from the pulser coil as Ren suggests.
2. Time the length of the pulse.
3. Measure the attack slope of the pulse ie how long it takes from 0 volts to maximum.

I'm sure all of these can be incorporated into the hardware quite easily (although personally have no idea of how) and probably can be adjustable by using appropriate varfiable resistors.

04/09/2023 11:26:18 UTC
nab301 said :-
Interesting comments on the workings of cdi units . Ian mentioned Boyer units and while I never used them I know plenty who have on more modern Enfield singles which were equipped from the factory with points ignition until the mid noughties. Strangely , from what I've read about these units they appear to revert to full advance if battery voltage is low which can be problematic for legs/ ankles if kickstarting or sprag clutches if using an electric starter.

04/09/2023 12:49:48 UTC
Ian Soady¹ said :-
I had a Boyer on my Norton Commando and it was great - well most of the time. I did go off it on a French trip where I spent hours trying to find a carb fault which turned out to be a poor contact on the horrible pre-insulated crimped bullets which Boyer saw fit to use. Actually, I'm having a déja vu moment as I've just gone through a very similar process with the XBR. I was convinced it was a carburation problem till the bloke who recovered me when I'd broken down told me it was the CDI when I described the symptoms.

As Nigel says, earlier versions of the Boyer system like the one on my Norton did default to full advance with low battery but I understand the later digital ones have cured this.

05/09/2023 11:41:18 UTC

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