DM450 MK3 ignition Fault

[DucRedux]

My 74 Ducati 450, which I have owned since 1974, has developed an ignition problem. This model has a CDI unit with Hall sensor as the ignition trigger and a 6-volt electrical system.

The bike starts reliably on first kick and then runs, but if it stalls, it will not restart until resting for some time, perhaps five minutes or much longer. My troubleshooting has this list of individual checks: battery, HT wire continuity, spark plug change, wire contact inspection, fuses, and swap with a new CDI unit from my spare parts. With the spark plug out of the engine and grounded, I have observed spark on the first engine turn over, but then no spark on subsequent turns. In other words, it has, I believe, replicated the starting failure described in the first sentence of this paragraph. The remainder of the electrical system seems to be functioning normally and the new battery is fully charged.

My last few rides of 30 miles or more this past week went fine and there was no evidence of trouble, in fact the bike ran great. What can be the problem? I am left with several possible causes: a bad Hall sensor, a bad ignition switch or connection, or a wire broken internally. (The running bike has had no stutter or cutting out as has happened with my BMW when the hall sensor went. And as you readers know, these bikes vibrate when started and shake connections all the while they’re running.) Further, the wiring diagram for this model is not in the Ducati Manual and the approximate diagrams for a CDI scheme which are on the internet from Mototrans and Electrex are general and may lack wire color indication.

Can some of you offer a diagnostic approach or possible cause? Thanks.

[graeme]

Which CDI ?
The original red box ?
Fed by the single winding on the alternator ?

Graeme

[DucRedux]

Yes, Graeme, the red box. I just tried to post a photo, but failed. The alternate tried is a unit bought in Italy and can be seen on this website:

https://www.scooterworks.com/Ducati-CDI ... c2EALw_wcB

I switched back and forth and the red box did give a spark on first turnover.

I have not traced wiring to the alternator yet, and the rectifier is a black cube replacement from Syds in Florida bought 10 years ago.

[themoudie]

Aye DucRedux,

In 1976 my 1974 450 MKIII did similar tricks, whilst I was trying to move from England across to the Isle of Man. At the time I had no money and on arriving on the ferry in Liverpool (pushing the bike on from the railway station! ) I was befriended my a Manx resident, who knew someone who could help on the Island. In short, as spares were not available in the Island and I was without money, the whole ignition system was removed and replaced with a ubiquitous Ford Escort set of points, mounted on a home made plate and with a Escort distributor cam and set at 28°BTDC, with an MZ condenser and 6v coil, powered from the battery. Kickstarting was interesting, but bump starting worked and once under way the timing was not a problem.

It wasn't until I rebuilt the engine 3 years ago that the points system, with a Ducati AAU fitted caused great pain (thread on this forum) and after 20 months struggling to get the engine to run the whole points set up was replaced with an Electrex Hall effect sytem and the starting and running faults were cured in one fell swoop! No blowing the carb off the inlet stub, with sheets of flame, a steady 1,100rpm tickover, good pick up and excellent spark through the rev range.

So my advice wouuld be not to mess about, as 48 year old insulation on the stator coils, will not be in the best of condition and in my experience Italian 1970's - 1980's wiring, has by now, started to corrode within its insulation from the connectors inwards. Purchase an Electrex set up and re-wire the "Old bird" with some modern thin insulation wire (11Amp), using tinned soldered and crimped connectors, with soft flexible insulation covers and heat shrink insulation.

The CDI/HT coil unit that you have purchased I believe is a #32398112 Ducati enorgia. These CDI/HT units have a minimal advance curve as they are designed for use with 2 stroke engines and the original Ducati trigger plate on the right front of the Ducati timing cover may not have sufficient adjustment to enable 28° BTDC advance to be obtained. At present I am wrestling with a 1979 Moto Morini 125H single that has severe ignition issues and a "suitable" replacement CDI/HT unit is this same one, according to the German Morini Owners and Moto Morini Club Nederland. However, the advance required by that engine is 36°BTDC @6,000rpm! Problem is that there is insufficient adjustment in the stator plate movement to achieve this factory figure. In my case the original CDI/HT unit doesn't appear to be the problem as the fault appears with either CDI/HT unit.

Where abouts are you, in case somebody lives fairly close bye? Remote electrickery diagnostics can be fraught, at the best of times. As I know to my cost!

Good health, Bill

[ducwiz]

I agree with Bill. You purchased the wrong CDI unit, a 2-stroke version without or with a very limited advance angle. This one
https://www.ducativintagestore.eu/trasduttore_centralina_per_accensione_elettronica_per_ducati_carter_larghi would have been correct.

Imho it is very difficult to find out why your ignition fails with this strange symptoms. At least, it seems not to be a thermally driven issue, because you can ride many km once the bike could be started. If you lived in my country and close to my town, I would offer a measurement campaign in your or my garage. I have a lot of electrical meas. equipment available in my workshop, DMM, analog and digital oscilloscopes, HT testprobes, clamp ammeter, etc.

Early in 2022, I worked on a friend's 250SCR with the same Ducati ignition, which had lost it's spark. Finally, we found a weak insulation in the alternator's power coil sourcing the CDI and in turn the power voltage for the CDI box was too low. Consequently, the Ducati system was entirely discarded and an Electrex STK-164 installed. Result: the bike is now a first-kick starter with a very constant idling, and runs great again. The Electrex is not a bargain, but worth every €, $ or pound.
On the other hand, it could be unneccessary to spend this amount of money, if the failure is based on a weak connector, broken wire etc., which can be fixed easily once identified.
I attached a wiring diegram for the w/c singles with a CDI of Ducati Elettronica.
And btw, the pick-up/sensor is not based on a Hall element, it is a magneto-inductive device containing a coil, a resistor and a diode as well.

wd-ducati-Ducati-CDI.jpg

cheers Hans

[LaceyDucati]

Any ignition switch issue can easily be tested by disconnecting the green wire from the CDI unit leading to the ignition switch. This green wire is the grounding wire for the CDI which is earthed with the ignition switch when in the off position. With it disconnected and insulated the ignition switch is out the circuit, however to stop the bike you will need to earth the green wire. Probably an unlikely issue but worth eliminating.

Bill, I'm sure an Electrex stk169 could be made to fit your Morini very easily. Bit of machining and maybe an adaptor plate.... Ignition on these bikes isn't rocket science, remember Bosch, Lucas, Boyer, Pazon, Newtronics and Electrex all use the same amplifier for a wide range of models and applications! Obviously Two stroke applications are going to be very different.

Nigel

[DucRedux]

Thank you, Bill, Hans and Nigel, for the prompt and thoughtful responses. I was wondering whether I have finally reached the point of major rewiring and parts replacement. I’m used to chasing gremlins in the old bikes that I have and this Ducati has had very few issues. I did not expect this to happen while the riding season is in full swing here in the Catskill Mountains in New York!

The correct electrical diagram is most helpful, Hans, and will now supplant my handwritten notes.

There are no specialists at all in the immediate area and I rely on my garage, suppliers, contacts like you and folks I meet at rallies and swap meets for information, help and motivation. It is appreciated. The replacement CDI I mentioned came from a Ducati shop Bologna a decade ago when I asked the proprietor what I might need in the future – insightful.

Over the past year, I have placed 12v Electrex charging systems in narrow case 250 and 350 engines and was planning to convert the wide case 450’s system to 12 volts anyway, so that lighting and signaling could be improved. It would seem that this changeover is coming very soon to include a new ignition.

P.S. I’ll be heading to Imola in September with my brothers for a reunion and the Mostra Scambio. I wonder whether any of you or other readers might be traveling there as well?

Thanks again
Dan

[Eldert]

Hi Dan

my brother Peter and me will be at Imola to . a whole busload Dutch buyers are Imola bound .

the Dutch Aermacchi club is chartering a double decker bus . i have been on that bus ever since 1989 .

Regards Eldert

[themoudie]

Aye Dan, pleasure to be of assistance as I know how vexing these things can be.

Aye Nigel, thank you for the encouragement. When I spoke with Electrex, I received the "Sorry mate, we don't do anything for that engine." reply.

I have also spoken with Boyer and some of the scooter tuning shops, but all have given me a negative reply to my enquiry. I shall be contacting the scooter ignition specialist, who at present has all my ignition parts and the original parts for testing using a jig, oscilliscope, etc. that I do not possess. I had replaced everything possible and thentried different permutations of components, in case the trigger coil was upsetting the CDI/HT unit, all to no avail. A direct email or phone call to you may happen after I have had the conversation on the health of my current system.

Your suggestion that an Electrex STK169 mounted on the 125H stator base plate might be possible, is a positive thought. The stator appears very similar to the Ducati, Lambretta and Vespa generators of the period, but the machined cutaway for the timing belt appears to be the major difference. The saying "What was made by man, can be repaired or replaced!" keeps me persisting, with the wee beastie.

Good health, Bill