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Discussion Starter #1
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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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.
 

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Discussion Starter #3
@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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Please do not use that gear puller on a flywheel. :jsm: 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 :drummer: you can service the advance mech, service the points, test / replace the condensor, and check for broken coil windings.
 

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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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Discussion Starter #6 (Edited)
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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Discussion Starter #7 (Edited)
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.
 

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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.
 

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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.
 

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Discussion Starter #10
@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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I believe I see a bit of bare wire from the left side coil to the condenser.....could be your problem. Points don't appear to be in very good condition either.
 

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If it was running hot that could mean a timing issue.

Your ignition definitely appears to be a Dansi. They are top quality for the day but now they are all 50 years old or more.

The advance mechanism on the Dansi mag is a high wear item... and critical to good running. It needs to be maintained properly. If it sticks it will run poorly, or if your base timing is too advanced it may run hot or burn a hole in the piston.

No matter what ignition you use, make sure you check timing with a strobe so you know where your motor runs at full advance. We get good results with a battery-powered one that looks like this.
 

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Discussion Starter #13
"New" stator with coils, condenser & points arrived today.
Doesn't look much better than the existing one but at least I have some spares to try.
The Condenser appears to be doing its job as I strapped on a multimeter and watched it lose Ohms.
 

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Ahhh...that glob of tape in the wire from the points to the condenser is where I saw that bare wire ion your stator. Perhaps subject to rubbing on the flywheel? or arching to the body of the condenser (ground).

Pretty basic magneto. Look for simple fault (bare wire dirty/pitted points).
 

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Discussion Starter #15
New wire arrived yesterday, just waiting on NOS points now and I'll try to fit it all back together.
Watch this space!
 

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Discussion Starter #16
Ok, it didn't work. I rewired anything that looked dodgy and replaced the points but still nothing - not even the tiniest blue flash from the points. I'm wondering how I can isolate the fault now. One or other of the coils? The condenser? I confess I'm a pretty poor mechanic but I'm keen to try. How/could I diagnose with a multimeter? Here's a photo of where I'm at.... I know, the soldering's amateurish but though ugly, it holds.

 

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Make sure you didn't refit your points grounded, that will ensure no spark. Check the fiber washer location.

Have you also swapped to a new or different coil?

Plug lead is fresh?

Non resistor cap?

Always disconnect the kill button until the bike is running well.

:popcorn:
 

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Hi Jon,
The light coil must be wired with coarse copper wire and the ignition coil shoud be wired with very fine copper wire. On the picture the two coils seems to have the same coarse wiring !
Could you verify with your old magneto coils if this is correct and if the new magneto is not fitted with two ligting coils ?
On an other way, the shape of the right coil seems weird and not according with the shape of the left coil, they must fit with the "inside circle" of the flyweel.
Regards
Dominique
 

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It does look as though the points are grounded at the "leaf spring" portion that carries the moving contact current. Us a low impedance ohm meter and make certain your points are "opening" and "closing" electrically.
 

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in order:
1. validate that the points are working as expected. with the flywheel off, use a multimeter set to continuity (and set to "beep") place the leads (or use alligator clips) on the two arms of the points.when the points are closed, it should beep, when the points are open it shouldnt. as mentioned before there is a fiber washer that isolates the moving fiber arm and spring from the body of the plate(earth/ground). if there is continuity with the points open, you have a short somewhere or, the fiber isolator isnt doing it's job. check this first.

2. GTW36 mentioned that the coils look like 2 ignition coils. the lighting coils of your replacement plate look wrong. its hard to tell what is the original set of ign and light coils from your pictures. the coils in the second pic definitely look wrong. both coils should have be of similar dimensions, but the lighting coil will have larger diameter wire. maybe you put 2 ignition coils on your new plate?

3. once you have spark, buy a new condenser. relocate it somewhere(like under the tank, next to the coil). old condensers have a tendency to break up when hot. under the flywheel is a bad place for a condenser.

i dont know this specific bike, but if it is like most italian magneto ignition bikes, it has 3 wire output from the stator. like this one: http://www.motoscrubs.com/Ducati_Electrics/magneto.pdf
 
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