125 WITH NO SPARK

Lambertini era singles (125 and 250 - half v-twins)
andygrew
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Location: Martock, England

125 WITH NO SPARK

Post by andygrew »

! have just purchased a 125 in quite nice condition for my granddaughter to learn to ride on.

I was told it started but cut out in a short distance - it doesn't, as it won't start at all!

Thought it would be fuel blockage as it had been standing a while, but it turns out it does not have a spark. I have a 350 and a 500 so know the usual causes, but does anyone know if there is anything specific to 125's I should be aware of?

Many Thanks Andy
hendre
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Re: 125 WITH NO SPARK

Post by hendre »

with the 125 the iginition system is differrent. The pickup is on the stator.
I have some documentation specific to the 125H/T, i can send it through wetransfer
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andygrew
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Re: 125 WITH NO SPARK

Post by andygrew »

Thanks Hendre, I have today found the problem - the transducer was faulty. I went through everything and got it going briefly a couple of times on the original, but it only ran for a couple of seconds. Swopped the transducer and it started second kick!

I have now run out of original transducers - in case of future problems do you know of anyone who can mend the faulty boxes or provide replacements?

Also do you know of any replacement systems as I have only been able to find kits for the 350/500.

Andy
Steve Brown
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Re: 125 WITH NO SPARK

Post by Steve Brown »

Don't bother looking for original transducers, get one of the Vespa ET125 types. They are good and more importantly new. Cheap too, the Chinese copies are worth a risk at about £15 on ebay. So far I've only bought the £30 odd types from Beedspeed, but all of them were good.
I personally would go that way rather than looking for a replacement system that probably requires a 12 volt conversion when your daughter will most likely want to get another bike after passing her tests.
Whichever way you go-good luck and I hope it works out. We need more youngsters on bikes and more of them ought to be female too!
All donations to the rest home for old Camels, Leicestershire.
andygrew
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Re: 125 WITH NO SPARK

Post by andygrew »

Thanks Steve, I'll definitely give one of these a go, as the replacement is 40 odd years old so may have a limited life. I
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themoudie
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Re: 125 WITH NO SPARK

Post by themoudie »

A plea for information please!

I have a 1979 125H, with cast wheels and rescued from the Isle of Cumbrae in the Clyde, about 15 years ago.

When first purchased the engine was reluctant to pull above 40mph and the bike was put to the back of the workshop. This year after wrestling with a recalcitrant Ducati single for 22 months, it was the AAU that was faulty, I have tried to get the 125H up and running again.

After lots of assistance from Benjy Straw and Mark Bridger, in relation to resistance values, voltages etc. and to take them. (Remote diagnostics are not easy, when dealing with my limited electrickery abilities!) I replaced the original Ducati Electronica transducer (323921) with the more modern "equivalent" Ducati Electronica transducer (32398 112 21 02), purchased from BeedSpeed, I think only the first five digits are relevant? However, I can find no information as to whether the advance for this 2 stroke transducer is as great as that of the original transducer. Whilst the engine revved more cleanly, it would die once hot or after approximately 5 miles. Further testing showed the magnetic pickup to potentially be at fault so this was replaced with a 'pattern' Lambretta 12v magnetic pickup mounted on the 6th pole of the Ducati Electronica stator.

At present, the engine will tickover quite happily @~1,100rpm, but it dies when revved to ~4,300 rpm. When I try to engage the clutch the engine dies before taking any load! I am suspicious about the ignition timing at low revs and the degree of advance that is available from the replacement transducer.

Trying to time the engine using a Xenon timing gun proves fruitless, as before 6,000rpm, the revs at which the ignition is supposed to be advanced to 36°BTDC electronically by the transducer the Xenon tube stops flashing as the two stroke ignition providing a "wasted spark" appears to overload the guns circuitry. Using an antique Gunson neon timing light wired in series with the ignition lead, shows no advance in the ignition timing, before the engine dies. When timing the ignition, because the mechanical tacho drive is removed along with the right-hand engine case, I have no way of knowing what revs the engine is at?

Does anybody know what the static timing is for a 125H? The NLM 'Blue Manual' does not contain this information and vaguely describes "....punching timing marks on the stator plate and engine crankcase....", once the ignition timing has been set at the requesit 36°BTDC @6,000rpm! Not much use if you cannot measure, or appear to achieve those parameters in the first place. :evil:

What is the advance curve programmed into the Ducati Electronica transducer (32398 112 21 02)?

Are there any other tests or methods that I might try to set the ignition up?

Does anybody have any experience and or data for the 'BGM' components from Germany? Link:BGM_tuning_ignition_components_for Vespa_&_Lambretta

My final resort is to replace the ignition coil on the stator or have it professionally rewound. But, as I seem unable to get the engine to run under load now, I cannot check to see if the insulation on that is breaking down after a period of running.

Thank you for your time to read this. The culprit below is living up to it's bye name! :twisted:

Desperate Dan Bill! :oops:
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mbmm350s
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Re: 125 WITH NO SPARK

Post by mbmm350s »

Hi Bill

The 323921 (as also used on 350s and 250 twins) has an internal resistor of 68 ohms.
see here:
https://www.motomoriniclub.nl/tech.html

The replacement most likely has an internal resistor of 480 ohms or thereabouts being more normal for the scooters.
(500 with its lower advance need has 270 ohms)
The transducer resistor acts like a potential divider with the around 100 ohms of the 125 (scooter) pickup, so the higher the value the more volts
and so the more advanced the ignition.

If you do not adjust the position of the pickup on the crank , then the timing will be out by the difference of the normal scooter advance 18-23 degrees to the 125H advance of 34-36 degrees of crankshaft rotation. It will be too advanced by around 14-18 degrees of crank rotation
Therefore to start you need to move the pickup to retard the ignition by at least 12 degrees - you can calculate this using schoolboy maths, or by proportion of ANT to PMS(0) on the rotor periphery.
Any tendency for the revs to hang on light throttle opening is a sign of over advanced ignition. This is common when fitting blue transducers to 350s without accounting for the advance.
The advance curve itself is fine and is controlled more by the magnetics of the pickup and capacitances within the transducer.

Once the position of the pickup is confirmed the loss of power beyond a certain RPM can be due to insulation breakdown (voltage induced) or partial collapse of the magnetic field, this could be caused by short circuit caused by faulty regulator in the lighting circuit, so i would disconnect the battery to be sure. The rotor can be re-magnetised - Paul Compton (Evguru) can help.

I use a cheap in line strobe gun on Morini instead of inductive clamp

Cheers
Mark
mbmm350s
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Re: 125 WITH NO SPARK

Post by mbmm350s »

The actual rpm for advance is not so important - wind it up till it stops advancing, which it will do at about 6000 rpm,
providing the pickup is nominally located correctly.
Ignition generator coils can be purchased as replacement parts for scooters (not suitable for twins as need 2x power - wasted spark consumes virtually no energy)
Mark
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themoudie
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Re: 125 WITH NO SPARK

Post by themoudie »

Aye Mark,
Therefore to start you need to move the pickup to retard the ignition by at least 12 degrees - you can calculate this using schoolboy maths, or by proportion of ANT to PMS(0) on the rotor periphery.
My Achilles heel, maths, arithmetic so, so, but trig, algebra, etc. difficult! I think that I am going to have to get my head round that bit! :oops:

On the 'original' timing mark the throttle pick-up is a bit woolly, but once opened up, the engine picks the revs up to ~4,500rpm, were it just dies a death, consistently. Before fitting the new magnetic pick-up this ~4,500rpm limit wasn't present and 6,000rpm could be achieved easily, even though without an engine load it hurts my sensibilities.

I will disconnect the battery to see if this removes this rev limit.

As for "re-magnetising the rotor", each magnet appears to be strong, as I can hang a large ring spanner from each magnet, without effort? I too have the old Gunson neon in-line timing light, but there is no advance whatsoever, within the rev range that I can achieve at present.

I will try and get my head around the maths and report back on the results of the various stages.

Thank you for your time and patience.

Good health, Bill
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Ming
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Re: 125 WITH NO SPARK

Post by Ming »

I don't know if this makes more sense to you? If you take the standard set point as your zero mark, moving it 1/4 turn would be 90deg, so 1/8 turn 45 and 1/16 turn 22.5, then 1/32 is11.25. ie if you advance the pickup 1/32 turn you are in the right ballpark - If you draw it out it looks simpler. If you are a nautical man, think points of the compass.

Or is that a load of ballocks?
mbmm350s
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Re: 125 WITH NO SPARK

Post by mbmm350s »

Hi Ming,
Sounds right, but now I am thinking that 12 degrees is along way to shift a crank mounted pickup, as its part of the stator, for the cam mounted pickup its only 6-7 degrees we need to move the pickup for the "blue" scooter transducers and that's always acheivable.
Nevertheless since ANT1 to PMS1 is 34 degrees (or 36 I don't recall for 125) isnt it simpler to put a tape on the flywheel periphery and determine 12 degrees that way

Bill,
On the 'original' timing mark the throttle pick-up is a bit woolly, but once opened up, the engine picks the revs up to ~4,500rpm, were it just dies a death, consistently. Before fitting the new magnetic pick-up this ~4,500rpm limit wasn't present and 6,000rpm could be achieved easily, even though without an engine load it hurts my sensibilities.
I didn't grasp that, so there is no problem in terms of failure to rev with the old pickup/transducer combo, or old pickup new transducer combo, then surely the fault is the generator winding breakdown? In any case a new scooter pickup must work with a new scooter transducer if the generator winding is good OR there is a carburettor fault!
New transducers (32398112) are more powerful and hence require more energy from the generator.
Dont panic about 6000 rpm!

By the way some later I think 2013 on scooters have mandatory rev limits for Euro compliance, Your friendly scooter shop can advise, so we are using transducers for the PX125 etc. I use wasp performance.

Magnetism sound ok too me if it will hang a hefty spanner from each pole, and its important that its each pole.

Mark
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Ming
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Re: 125 WITH NO SPARK

Post by Ming »

mbmm350s wrote: 16 Sep 2021 09:02 ... isn't it simpler to put a tape on the flywheel periphery and determine 12 degrees that way?
Yes! Mark the tape in thirds and you have 11>12 deg (or about 3 points off the port bow...).
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themoudie
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Re: 125 WITH NO SPARK

Post by themoudie »

Mark and Ming, thank you gentlemen, I think I understand the process! :oops:

But and it's a BIG BUT, which way do I need to move the stator? Moving the stator to the right (clockwise) when viewed from the right-hand side of the engine, I think, as the direction of crankshaft rotation is clockwise? :?: This will retard the ignition, according to the Blue book'.

According to the Blue book, @6,000rpm the ignition spark should be created @36°BTDC for the 125H engine

So, in my numpty fashion I'm thinking that I need to rotate the stator to the left (anti-clockwise), by ~12°, to increase the advance of the transducer producing the spark from it's electronically set 18° - 23° advance, when the factory marks on the stator plate and the crankcase are aligned, to produce the ~36°BTDC of ignition advance required? :?: :oops:

Please would you clarify the direction of movement required of the stator base plate, clock or anticlockwise?

I am happy to mark out graduations on the crankcase web, on which the stator mounts, in either clockwise or anti clockwise direction from the factory mark, so that I can achieve at least the extra 12°of ignition advance required.

I too was thinking that the ignition generator coil was breaking down under load and the reason behind the current ~4,500rpm revs ceiling. The carb was rebuilt with all new parts from Eurocarb and the mixture was producing a tan ring around the nose of the central electrode porcelain, with no signs of overheating. I may need to richen the needle by a notch, if the ignition can be sorted out.

I bought the transducer from BeedSpeed, but will see if Wasp Performance can supply a suitable ignition generator coil. I have also seen one advertised by Torbay Lambretta and on BeedSpeed's website. The problem can be my reliance on the person at the dealership knowing what is required from the information that I can supply, without actually holding the part. Moto Morini using unmarked scooter stators behind a Ducati Electronica flywheel that has a part number (31.96.91) could cause allsorts of misunderstandings.

Thank you for your time and patience, Bill
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Ming
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Re: 125 WITH NO SPARK

Post by Ming »

To retard the ignition, in effect you need to move from ANT towards PMS if I understand Mark correctly, so that you would make a new timing mark approx 2/3 of the way between PMS and ANT in this instance.
Please wait for confirmation, though...
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themoudie
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Re: 125 WITH NO SPARK

Post by themoudie »

Morning Ming,
....in effect you need to move from ANT towards PMS if I understand Mark correctly....
That is why I find this sort of modification not easy.

I think that I do not need to make any new marks on the periphery of the rotor. The current ANT timing mark on the periphery of the rotor appears to be at 36° BTDC, so in my thinking that doesn't require revision. ANT, as currently marked, must line up with the axis of the camshaft when the ignition spark is delivered at the transducers circuitry fully advanced capacity. As the replacement blue transducer,Ducati Electronica transducer (32398 112 21 02), has LESS of an advance range than the original transducer, I need to move the magnetic trigger coil/stator plate to compensate for this difference.

So, I need to create a new mark on the crankcase that indicates where the stator and hence the magnetic pickup's angle to the crankshaft gives me 36° of ignition advance @6,000rpm, not the new transducer's 18° - 23°, which would be the case if I revised the ANT mark on the rotor anti-clockwise by 12°.

In my birth counties vernacular "Thasan awfa lot a squit bor, if yer head has it wrong!" :lol:

Thank you for your time and input, Bill
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