No Spark on the 150 - MVAgusta.net
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post #1 of 15 (permalink) Old 11-01-2017, 03:02 PM Thread Starter
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No Spark on the 150

Having removed the flywheel and checked all the wires were connected, replaced same, ascertained that the points were opening and closing as they should, I thought I would try for a spark. Was there one? No there was not! There are two wires coming out of the generator, one red the other black and if what I read on the net it’s the red one I need, this is connected to one side of the coil, while the other goes to earth. The coil was made by “Fenoy” and is stamped on it’s base 6 3 8 ( the date possibly, the bike left the factory in Oct 1968) and the two terminals are marked 15 and 1. Which way round should they be connected? I did try swapping them round, it made no difference at all. If in fact the coil is dud can I simply replace it with a regular 6v coil that my local motorcycle accessory shop will have, or is it something special, peculiar to these machines? Winding the engine over with a brace produced about 2 volts at the coil terminal. Any suggestion welcome.

Last edited by Jacks the Lad; 11-01-2017 at 05:24 PM.
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post #2 of 15 (permalink) Old 11-03-2017, 01:00 AM
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The wonderful world of old school MV electrics - progressively I am changing all mine over to electronic ignitions, then you have "start every time I want ride" reliability! But short of that diagnosis of the old school black art of 'electrics' is quite the challenge.

Ok..things to look for:

1. While the points are opening and closing as the should is the gap correct? If wrong, no spark. I don't know the factory gap setting but measure it as it and see what you get - somewhere between .3 & .4mm could be correct but obviously if it is .5 or .9 it will not be correct.

2. Check coil (lots of great reference points on the net, YouTube etc that will walk thru how to do it) - you have an amp meter so good start. If it is a dud, a replacement coil should be available, many of them have multiple applications but you have check it is correct for your application.

3. Check Stator - check visually broken wires etc copper damaged etc and then check with amp meter ( again heaps of great reference available)

4. Is motor in situ and all wiring attached? If so, check for short in kill switch wire or even the kill switch itself.

5. Ignition switch (as above)

and that's by no means an exhaustive list - hence why most people (and mechanics) avoid electrical problems like the plague

Good luck!


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post #3 of 15 (permalink) Old 11-03-2017, 06:15 AM
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Question, as I do not know.... Are the older MVs battery ignition or flywheel magneto?

I know most small bore bikes from that era are flywheel magneto, and even some large bikes had magnetos, though not usually flywheel type.

On flywheel magneto ignitions the charge coil is the usual culprit when there is no spark. Test it for proper resistance (typically a small value like 5 ohms) and insulation to ground. Since on end of the coil is grounded this means you have to disconnect that end, which may mean de-soldering.

Point gap is a function of dwell angle (how long the points are open), which is instrumental in how much energy is built up to fire the coil.

In my experience, the ignition coil itself rarely fails. The charge, or stator coil(s), are mounted on the engine case and therefore subject to vibration and high heat. That is where most problems come from. You probably have 2. One for ignition and one to generate a charging system voltage or lighting voltage on bikes with no battery.

Using a peak reading voltmeter to measure the charge coil's output is useful to. A basic voltmeter will give erroneous readings.

This also holds true for crank position sensors or "pulse coils/pick-up coils" on EFI and CDI/TCI ignitions. They're the ones getting heated and vibrated during operation.

Wish I was near by to help. I love electrical problems. Great puzzles to solve.

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post #4 of 15 (permalink) Old 11-06-2017, 07:34 AM
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Some good suggestions posted but here's a couple of things I found when restoring my Cyclemaster.
1/ The HT lead was soldered to the lighting coil! Can't happen with secondary remote HT coil but the point is "check the wiring" Don't assume it's correct, as it may have been tinkered with by someone who didn't understand what they were doing.
2/ Check the flywheel key is not partially sheared as it's important the magnetic flux is at its peak when the points open. My Cyclemaster had a very weak spark that wouldn't fire, until I fitted a new key.
Check your spark from the bare end of the HT lead. It needs to jump 4 to 5mm in air to fire under compression pressure.

Maybe you could post some photos of your mag? My CS57 has been converted to Power Dynamo but I've got all of the old bits.
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post #5 of 15 (permalink) Old 11-08-2017, 05:49 AM Thread Starter
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Here is a photo of my back plate and stator coils, one coil for the lights, the other for the ignition I am guessing. Can’t check the wiring as has been suggested, there isn't any- some previous owner has thrown it all away – along with all the rest of the electrics. I am temped to just go for the more simple battery – coil - points set-up which at least gives constant (as long as the battery is in good condition) voltage to the ignition and is not dependant on the engine speed. On the other hand would the single lighting coil be up to the task of running the lights and ignition? I note that the bike only had a 20 watt head light so maybe MV weren’t expecting too much from it in the first place. From a diagram that I found on the net there doesn't seem to be any sort of regulator, maybe that's why. Replacing the ignition coil with another lighting coil (if I can find one) and combining their outputs would would give an improved output but would then almost certainly need some form of regulation, solve one problem cause another.
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post #6 of 15 (permalink) Old 11-08-2017, 06:00 AM
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The coil on the right looks to have been rewound at some time. The condenser looks pretty dodgy. Should be easy to find a replacement (not really a "special" item). Might it be shorted?

From looking at your photo I think the coil on the left (the old one) is the lighting coil. The question I have is where is the ignition source coil (I think that is the one on the right) grounded? One end of the coil should be grounded, the other leading to the points.

Tying the 2 coils together for the ignition isn't going to work/help. Has a lot to do with the AC waveform generated as the magnets move past the coils.

One more thing...the wires connecting to the points must be insulated from the base plate. It looks like they are screwed straight to it. Can you register the open and closed circuit of the points with an ohmmeter?

Good luck.

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post #7 of 15 (permalink) Old 11-08-2017, 07:53 AM Thread Starter
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The two coils are in effect two AC generators and unless their outputs are in phase – and there is of course no guarantee that they will be - there could be, depending on how much out of phase they are quite large circulating currents. Would need to take their output via a rectifier each before joining them up, sorry should have been clearer. In the meantime I will take the back-plate off and see how everything is connected up, Will report back latter

Last edited by Jacks the Lad; 11-08-2017 at 08:51 AM.
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post #8 of 15 (permalink) Old 11-08-2017, 10:32 AM
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If the 2 wires connected to the points and the spring from the moving contact are not insulated from the points base and fixed contact (sure looks like they aren't!) then you will never get a spark. Maybe that's all you need?

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post #9 of 15 (permalink) Old 11-08-2017, 11:44 AM Thread Starter
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OK as promised I removed the back plate, the wiring is thus :- Two wires are connected , one black the other red. The black goes to one end of the lighting coil, the other end being bonded to it’s bobbin which is in turn bolted to the back plate so is in effect connected to frame. The other coil has one end bonded as before, the other is connected to one side of the points, also connected are the capacitor and the outgoing red wire. In use it would appear that when the points are closed this coil is shorted out. One side of the points (the movable part) is insulated, the other bolted to the back plate.
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post #10 of 15 (permalink) Old 11-08-2017, 02:34 PM
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OK, a few suggestions:

1/ If you haven't already, then I suggest you have a look at this post and check your wiring is the same.
http://www.mvagusta.net/forum/14-cla...on-system.html

2/ When you say, "one side of the points is insulated", do you mean the arm is insulated by the brown bakelite or the wires are insulated from ground where the connect to the moving point? I agree with esq' me that the wires don't look correctly insulated. There should be a fibre washer visible each side and one of them has a boss that goes through the metal mounting to prevent the screw from shorting to ground - see photo below.

3/ I've checked in the spares that came with my bike and I have a Dansi stator set-up. It's off a 175cc CS57 (from 1957!). The previous owner told me he had it refurbished (£200 he said!) and then decided to fit a Power Dynamo unit. That explains why the primary coil is not actually connected, the wire is just looped through a hole.

4/ One final thought. The points cam could be on backwards. On my Cyclemaster it's a slide fit, keyed in position like yours but can be fitted 2 ways - one works; one doesn't. The CM cam has a very feint arrow showing direction of rotation. Might be worth checking.

My stator unit has the points facing the other way but that's probably because it's from a different model.
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Last edited by Mondello175; 11-08-2017 at 02:39 PM.
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