Mk3 250 Starting Issues

[Jordan]

It may be that the important question is how much it will cost to have it running well again.
If considering points (a.k.a. the Kettering system), it should be reassuring that Ducati did a nice job of theirs. It's not flimsy in its mounting method, unlike some Lucas types of the '60s. And the advance-retard unit and the points themselves work fine. Definitely don't use the original HT coil though. I've never had good results with those in any of the six singles I've owned. Just about any other brand of 6V coil would be much better. I've even used VW Beetle coil & condensor, but they're quite big. Ducati and Motoplat pointless CDI systems don't rely on the installed battery to work, but you'll probably need one for points.
It might be worth mentioning that points can be also used to trigger a separate elec ign system. Some swear this is a great system, allowing for quick roadside switching over to Kettering, if the electronics fail. Elec ign engines do seem to start easier.
Going back to diagnosis, I'm not sure, but maybe there's a method to check if the alternator's ignition charging coil is making enough volts, using a multimeter? I don't know what would be a normal reading though.

Jordan

[DewCatTea-Bob]

[quote= graeme ...
" Bob, Ducati Electronica were (as far as I'm aware) were fitted to the '74 singles.
The blue and yellow Mk3's, the last Scramblers and the yellow Desmo's. "

____ I'm aware of THAT-fact Graeme, (as I was the top-position employee at a Ducati-dealership back then, and I've owned a '74 450-Scrambler since 1981) !
__ What's been keeping me from getting on-track with what we're actually dealing with, is that I've personally been unaware of any stock 250-model (of any model-year) with a 12v.system !


Ignorant-Cheers,
-Bob

[Old Cog]

Graeme

Brilliant! Maybe I've just lucked out and the problems were down to a bad HT lead. Hopefully the ignition will be fine ...indefinitely.
I've got a B6HS and a spare (new) B7HS. A B5HS might be better for the way I'll use it but the seller a year ago told me the engine had a non standard !0:1 piston in it, which is also the reason why I'll hold off on the protruding electrode plug for now.

Jordan
If it turns out the ignition coil in my alternator is on its way out, I'll certainly look at putting points in. I would gladly test the output if I knew what it should be. Hopefully someone can point me to a source.


Bob

Apols for not responding to your original request to identify the carb. It's a Dell'Orto VHB29. I replaced the float needle and fuel taps soon after I got the bike when a three-week stand allowed the entire contents of a 3/4 full petrol tank to run down into the sump. (It was an embarrassing moment when I next started it up and it all started gushing out the breather pipe.) The choke cable needs to be clamped shorter because much of the choke lever movement is wasted - beyond what the threaded adjuster can cope with. However, the effect of putting the choke on for a moment when the engine is running confirms that the present set up does choke the air flow. I'll get around to adjusting the idle mixture and speed but I don't think fuel supply is currently an issue at starting.
Though the Ducati pointless system seems almost certainly an original fitment, there's no reference in Haynes to anything except 6 volt electrics as you suspect. But my battery is unquestionably 12 volts.
As to details of the machine, it is indeed a wide case model. It was first UK registered on 1 Jan 1975. So made in 74 - or maybe even 73? I gather the Electroticnica system was fitted to all the Mk3 and Desmo models imported here from 72 on. As to where else these versions of the bevel singles were exported to, I've no idea I'm afraid, but the blue and gold ones were popular in the UK. It was the first Ducati I ever saw on the road and just as pretty today. Here's a couple of pics

$_12.JPG

$_35.JPG

(These are from before I swapped it to regular footrests and bars. It's too wet today for decent pics.)
Starting procedure. I generally turn the fuel on, put on my gloves, turn the engine over twice, take it to just before tdc, pull the choke lever and jump on the kickstart. I haven't yet discovered what's best to do with the throttle on this bike when cold/hot- leave it alone or give it a good tweak just after you accelerate the piston. If I suspect it's flooding I'll turn the ignition off, open the throttle gently all the way and turn the engine over a couple of times if need be with the plug out. Is that not right?

[DewCatTea-Bob]

____ I had meant to get-around sooner to finish editing my last post on the previous-page, and had indeed begun working on doing so,, but because there's been so many newer posts that have since forced the creation of this new page, (and realizing that readers tend to ignore looking over pages prior to the newest), I've decided to rather post my completed edited-post over onto this-page instead.



[quote= Old Cog ...
" many of you may not know my model since jimF informs me that the blue and gold Mks was not imported to the US. "

____ Certainly not "250" versions ! _ But the '450 Mark-3' was on Berliner's availability list for 1974, (although every-time I ordered that model for our Ducati-shop, all we could get was just the Scrambler-version !).
__ From the start of your thread, you should not've withheld any such information of which 250Mk3 model you've actually been in reference to ! - (As it's frustrating having to shoot in the dark !)



" Maybe one detail mentioned is that the GEN indicator light is not clear but red. "

____ Then what color is it's high-beam indicator-light ?



" I find my ignition system is the Ducati Elettrotecnica. Probably installed originally "

____ I'm unaware of any stock Duke-single originally equipped with such an ign.system along-with it's associated alternator being used with a 12-volt system.
So is your Duke-model newer than 1974, -(the last year singles were imported into the USA) ?



" (There's evidence the engine has been tuned for racing - HC piston and twin plug head "

____ Interesting, sure would like to see a close-up picture of the right-side plug-location !
So why-not running any longer with dual-ignition ?
This enigma indicates that the ignition-coil(s) employed, must've had some sort of mixed history (which ought-to be investigated).



" Are there any tests I can do
of the dedicated alternator coil
(I've got a decent multimeter.) "

____ It would certainly be of related interest to check it's resistance-values (to learn if they've deteriorated much from stock/original-values) !
Also, the ign.power-coil's voltage-output at idle would be good to compare with a known good-working example.



" The problem Jordan had might well apply,
and the breakdown of insulation he describes could be going on. Though I can't be sure I quite follow all the pathways Bob describes "

____ When the air-gap that the high-tension spark-voltage is expected to jump is too great, the resulted even higher voltage-juice -(ultra-pressure electron-current) is then forced to find an alternate route to ground (instead of over the plug-gap). _ Apparently the next most likely least resistive (but unexpected !) circuit-pathway is for the spark-juice to force itself from the secondary-winding to the primary-winding within the ign.coil, and from there travel through the connected external primary-circuitry and on/down-ward to finally reach the ign.system's dedicated power-coil, where the high-pressure juice is still left extremely-determined to find the least resistive obstruction to punch itself through to ultimately reach ground ! _ And it apparently then finds the weakest point in the power-coil's insulation and literally punches infinitesimal pin-prick openings though the insulation (which of-course never heals, but can possibly grow larger).
Once the power-coil has been so zapped, the resulting leakage-pathway in it's insulation becomes permanently established,, and-so the normally generated-voltage produced by the power-coil itself can then become bled-down enough to weaken the charge of current that's depended-on to fully excite the ign.coil, thus the ign.coil is accordingly less compelled to produce sufficient spark-juice. _ And I imagine that as the detoured-down high-tension spark-juice continually pounds-away at the power-coil insulation,, it eventually gives-way and allows even more bleed-off, thus still further weakening of the ign.spark (till non-existence).
(The above explanation is the supporting scenario for the supposed diagnosis (of a zapped power-coil) which was submitted by Jordan (in his post on the previous-page). _ However, I-myself personally don't necessarily agree that this conception is actually likely, and would have-to personally examine the supporting evidence to really believe that it's truly possible to've ever actually occurred ! )
__ It's commonly known that an electronic-ignition system benefits the ignition-process with larger plug-gaps,, and while that's just-fine with electronic-ign.systems powered by a battery, these systems powered by a power-coil are apparently vulnerable to the results of plug-gaps that are any larger than the minimum recommended gap-setting. _ So thus one ought-to be kept aware of this factor (concerning power-coil powered electronic-ign.systems) and make-sure not to set their plug-gap too large !



" The big question is, "Does this mean I'm looking at/for a new alternator?" "

____ (Whenever I see someone use quotation-marks to try emphasizing their wording, I'm left wondering how they had meant for it to be taken exactly [since they're not actually 'quoting' anyone-else's stated-wording], but this is the first time I'm inspired to bother mentioning it.)
____ Anyhow, it's fairly doubtful that you'd need a whole new (or good used, [if possible to find]) alternator ! _ However if your alt.stator doesn't pass the tests (which can be done with a good multimeter), then you may just need to merely rewind the ign.power-coil.



" I'm also interested in Jordan's idea of going back to points. "

____ Before bothering to go that extensive route, you could first try another ign.coil with a higher turns-ratio, (so as to get-by with the [apparently] reduced current-output from the power-coil). _ And if that possible fix turns-out unfruitful, then next try substituting battery-power (in place of the power-coil's normally supplied pulse of powering-juice).



" I replaced the HT lead and plug cap. Better: still small and bluish but more regular. It MAY be enough
But it's not a healthy looking spark. "

____ So just how large do you normally keep your plug-gap set at, anyway ?


Duke-Cheers,
D.Bob

[Jon Pegler]

Where are you in the UK?
If you want to know a little more of the history of your bike send me a message.
I used to own it once upon a time.

Jon

[DewCatTea-Bob]

[quote= Jon Pegler ...
" If you want to know a little more of the history of your bike
I used to own it "

____ This is potentially very interesting ! _ I'm quite sure the current owner isn't the only one of us who'd like to know all about it, (especially the related story concerning how the duel-ignition was powred) !


Enlightened-Cheers,
-Bob

[DewCatTea-Bob]

[quote= Old Cog ...
" A B5HS might be better for the way I'll use it but the seller a year ago told me the engine had a non standard !0:1 piston in it, "

____ I believe the B5HS would be too hot (from absorbing the higher heat produced by the higher comp.ratio.



" If it turns out the ignition coil in my alternator is on its way out, I'll certainly look at putting points in. "

____ I still think you may possibly avoid jumping back to that desperate degree, by first trying my previously mentioned related suggestions.


" I would gladly test the output if I knew what it should be. Hopefully someone can point me to a source. "

____ While I can't provide whatever is the operating voltage-level of the ign.power-coil at any RPM, I might possibly be able to measure it's resistance-values (on my '74 450-motor), if no-one else provides their measured readings.



" It's a Dell'Orto VHB29. "

____ That's a nice carb.model that should provide you an advantage with getting the engine started, (compared to SSI or old Amal carb.models) !



" a three-week stand allowed the entire contents of a 3/4 full petrol tank to run down into the sump. "

____ Such similar (but much reduced) leakage is a common problem that often leads to scored cam-lobes & followers !



" much of the choke lever movement is wasted
However, the effect of putting the choke on for a moment when the engine is running confirms that the present set up does choke the air flow. "

____ While it's not too-awfully misleading to refer-to the handlebar-lever as the 'choke', the actual workings within your 'square-slide' carb.model is definitely not an actual choke-setup ! Rather, it's an enrichener-circuit that allows a richer fuel-mix into the intake-port, which is why the 'choke-lever' is turned oppositely from a real choke-slide setup !



" I don't think fuel supply is currently an issue at starting. "

____ Only a cold engine should require the 'starter-jet' to be fully opened,, and if all else is good-to-go, the engine should start-up by the second kick-start attempt !



" the Ducati pointless system seems almost certainly an original fitment, "

____ Having learned your Duke is newer than 1971, I now believe it indeed is.
Hopefully Jon will know whether it's still the very original, (since he's likely the one who once had the dual-ignition setup installed).



" there's no reference in Haynes to anything except 6 volt electrics as you suspect. But my battery is unquestionably 12 volts. "

____ A previous-owner was probably aware that merely switching-over to 12v.components & a 12v.regulator is all that's necessary to convert-over from a 6 to a 12 volt system. _ (But likely didn't realize that the RPM.point at which the 12v.battery can begin charging is raised a few-hundred RPM.)
__ You should check to see if they really knew what they were doing, as the associated regulator-setup might possibly not've been properly dealt with !
If you don't know for-sure by looking at it yourself, then post a picture of your regulator-unit's connections so we can then see what's-what.



" I gather the Electroticnica system was fitted to all the Mk3 and Desmo models imported here from 72 on. "

____ It seems that contact-points were eliminated from all OHC.models sometime in 1972.



" Starting procedure. I generally turn the fuel on,
turn the engine over twice, take it to just before tdc, pull the choke lever and jump on the kickstart.
Is that not right? "

____ Well, I-myself wouldn't normally try it in that order.
After opening the petcocks and seeing the fuel-lines stop flowing, I'd then pull the starting-lever fully-open, then position the piston as close to 'comp.TDC' as possible, then turn-on the ign.switch and WHOLEHEARTEDLY kick-though for intentionally completing the next entire Otto-cycle. _ And if that first attempt fails, then a second identical attempt right-after.



" I haven't yet discovered what's best to do with the throttle on this bike when cold/hot- leave it alone or give it a good tweak just after you accelerate the piston. "

____ (Back when I was still able to kick-over an engine), I'd most-often give the throttle a slight prolonged blip (which I think was most-often timed to begin about when the piston was next reaching the very-following comp.TDC).
If your cold engine fails to start by merely having just the choke-lever fully engaged open (with throttle left shut-down),, then try practicing that preferred timing for cracking the throttle open just a tad (or 'blip-it'), as I've learned works best.


Hopeful-Cheers,
-Bob

[Jordan]

" I'm also interested in Jordan's idea of going back to points. "

____ Before bothering to go that extensive route, you could first try another ign.coil with a higher turns-ratio, (so as to get-by with the [apparently] reduced current-output from the power-coil). _ And if that possible fix turns-out unfruitful, then next try substituting battery-power (in place of the power-coil's normally supplied pulse of powering-juice).

Lost me there, Bob.
Both the elec igns fitted standard to Ducati singles have special HT coils, with electronics embedded in with them. Not so easy to change the coils?
Battery powered CDI would require a step up transformer, to get the needed 300 or so volts to charge the capacitor.
Anyway, going back to points shouldn't be so expensive (extensive?). Many have been removed to fit superior (?) elec igns.

Jordan

[Old Cog]

Thanks Jon.

That would be great. Looking forward to your info.
I'm in Lancaster if you're ever by here maybe we could meet - or I'm in London now and then. (We could private message about meeting or a phone call.)

A machine with provenance!

[Nick]

”Starting procedure. I generally turn the fuel on, put on my gloves, turn the engine over twice, take it to just before tdc, pull the choke lever and jump on the
kickstart."

You may find that it starts easier if you move the piston to just after TDC on compression, this allows the crank to build up inertia before it comes up on compression again. Or, put the bike in gear and back it up on compression, then kick (this positions the piston/crank in a similar location. This method is also easier on the kickstart mechanism and requires much less physical effort.

My 350 starts very easily if I bring it to TDC on compression slowly using the kickstart, ease it a bit past TDC using the compression release, then turn on the ignition and kick.