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post #1 of 22 (permalink) Old 07-02-2013, 04:59 AM Thread Starter
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:: No spark

I'm sure this topic has been covered variously before but as we all know each model has its idiosyncrasies.

So now the good weather has finally arrived in the YooKay I am naturally beset with problems that stop me riding the beloved Flying Ant and leave me stranded on a traffic island waiting for the AA. This time it's spark.

Working backwards I can rule out plug, HT lead and yesterday coil as a replacement arrived which I swapped out. I was rather hoping it would be the coil and thought it might be as I had absentmindedly noted that the bike was running rather hot the previous journey.

I've double-checked the earth and can so no obvious break or damage to the section of wiring harness that runs to the points &c.

So now I'm wondering what I can check next to isolate the problem. I'm rather dreading removing the flywheel but I'll have to if I'm to replace points, condenser or stator. I do have a chunky old flywheel puller which I've never used:



There's bound to be tears before bedtime - there always is with these things. So if anyone could offer me a few kind words in the way of dos and don't or shortcuts to work out *exactly* how/what to replace (and what I may as well replace whilst I'm at it) I'd be enormously grateful.

I have seen an entire stator with condensor and points attached for sale which I'm considering buying:



Might be a gamble worth taking?

Any answers on the back of a postcard to the usual address....

Cheers in advance.
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post #2 of 22 (permalink) Old 07-02-2013, 06:48 AM
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I would try and offer advice, but not totally familiar with your beloved "Ant".

Is it just a simple magneto, or battery powered ignition?

First things first....check points for cleanliness or pitting. Use a "points checker" to confirm opening at proper timing and no resistance when closed.
Could be your "new" coil is defective. Check resistance on the primary and secondary and, most importantly, insulation if possible (this can't be done on some coils where both primary and secondary terminate at the core with no way to open that termination for testing).
Do the same with the source coils on the stator if it is a magneto...as well as check peak AC voltage generated (requires a peak voltage meter). Continuity of wiring from magneto to coil....

I'm sure it is something simple....as for pulling the rotor, pally wrench pressure to the push bolt and then smack it with a lead or brass hammer. Repeat. Do not just twist away on the bolt.

Good luck.

I used to be fast....now I just dream about it.
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post #3 of 22 (permalink) Old 07-02-2013, 08:35 AM Thread Starter
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@esq'zme Many thanks! I shall try to do what you suggest.
BTW> Yes, it is a simple magneto on the '55 TR
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post #4 of 22 (permalink) Old 07-02-2013, 08:33 PM
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Please do not use that gear puller on a flywheel. You need a puller that looks like this one.

First off, measure the threaded ID of your flywheel (is it a Devil, a Dansi, or is it a Marelli?) and buy the puller with the correct OD and thread pitch. On the 175 models w Devil or Dansi flywheels a puller like this made for Vespas and Bultacos works a charm. Maybe the same one will also fit your 125.

Once you have the flywheel off you can service the advance mech, service the points, test / replace the condensor, and check for broken coil windings.
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1954 MV 175 CSS Super Sport
1957 MV 175 CS Modello Sport
1967 Motobi 125 Sport
1974 Ducati 750 GT
Left Coast USA

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post #5 of 22 (permalink) Old 07-02-2013, 08:45 PM
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Sheriff,
That reminds me.... here's an MV 125 that I installed a modern ignition in just a few weeks ago, headed out for a test ride. It is an unrestored TR125 "Sport" (low bars, big brake, red paint). Cute!

Is this cute lil bug like your own Flying Ant?

It's not as fast as the "Sport" name implies. The owner would undoubtedly love to learn what your 125's top speed is, what the piston crown looks like, and what size carb it has.
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1954 MV 175 CSS Super Sport
1957 MV 175 CS Modello Sport
1967 Motobi 125 Sport
1974 Ducati 750 GT
Left Coast USA

Last edited by hulagun; 07-02-2013 at 08:51 PM.
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post #6 of 22 (permalink) Old 07-03-2013, 03:30 AM Thread Starter
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Ha! What was I thinking? It became obvious when I looked at the flywheel that I has the wrong tool to hand.
But luckily I DID have the correct flywheel puller which I had purchased from the UK club six years back and never had cause to use. It fits nicely onto the thread of what I believe is a Dansi wheel. I've nit had time to remove the wheel yet - slowly does it - but I'm confident it ought to work properly with a bit of care.
As to your second post, I am using a Dell'orto MA 16B carb with trumpet or F6 air filter. The jets and slide are stock recommendations from the DO carb manual. I estimate my top speed to be around 50mph - eind-assisted! I can send a photo of the piston crown tomorrow.... Thanks again.

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post #7 of 22 (permalink) Old 07-03-2013, 05:47 AM Thread Starter
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The picture above does show a similar bike. Handlebars are different (I like yours better!) as is the exhaust (prefer mine). You also have a steering damper and great-looking fule cap.

If this is a '56 Rapido Sport then it would require an MA18B with a 60 slide D12 needle 260B atomiser with jet sizes of 78 and 40 and a 6.5g float. I think also an F6 air filter.

Last edited by Sheriffof0; 07-03-2013 at 05:49 AM.
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post #8 of 22 (permalink) Old 07-03-2013, 08:28 AM
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Sheriff ....regardless of puller type (glad you have the proper tool") the "tighten fully, then whack with the hammer" technique is correct.

I used to be fast....now I just dream about it.
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post #9 of 22 (permalink) Old 07-03-2013, 10:25 AM
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Sheriff it occurs to me that your recent fuel filter troubles could be ignition related. If you have something going out in your magneto it could mimic fuel starvation.

The 125 in the photo belongs to a friend. It is very much a survivor, that is the original paint.


1954 MV 175 CSS Super Sport
1957 MV 175 CS Modello Sport
1967 Motobi 125 Sport
1974 Ducati 750 GT
Left Coast USA
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post #10 of 22 (permalink) Old 07-04-2013, 08:13 AM Thread Starter
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@hulagun Your sound advice has paid dividends! I have now separated the Dansi flywheel from the stator.
I did purchase the spare stator (pictured above) from a german eBay vendor for around 60 so I could at least have something to test against (assuming it works). But something is obviously unhappy down there so swapping out the parts will surely reveal the culprit. I also bought a NOS set of points for a few quid to make sure. When these arrive I'll swap them over and see if I can get some spark.

I think you're right about the fuel starvation issue being mimicked. I thought the coil was going because the engine was running so hot but now I know the coil is not the problem I suspect one or other of the stator components. I suppose I ought to renew the wiring whilst I have the can of worms opened. It's probably seen better days.





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