Vespa Ciao Magneto

Chris Robertson /

Hi All:

Anyone have any experience with 1972 Vespa Ciao magnetos?

I replaced the condensor and points in my Ciao, and accidentally disconnected a wire while removing the flywheel (I didn't have the special tool, so I drilled holes in the flywheel, tapped them out, and used an harmonic balance puller to get it off). I reconnected it where I thought it belonged (according to the schematic).

The timing is absolutely dead-on. I've quadruple-checked the schematic in my shop manual, and the wiring seems correct. I'm getting voltage for accessories (horn, headlight), but nothing is getting to the HT coil (I hooked up the wire that goes to the ignition coil to an AC voltmeter and got nothing).

I've checked the continuity of all my wiring, and I am stumped!

Anyone know of any "gotchas" I may have missed?

Thanks!

Chris.

Re: Vespa Ciao Magneto

Ron Brown /

Chris,

I am not familiar with the Vespa magneto, but I suspect that it works very much like most "energy transfer" systems (I got that name from my old, generic how to fix your motorcycle book).

This is easier to describe with pictures so imagine my hands and arms waving as you read this.

Inside the magneto are one or more coils which provide power to the primary side of the coil only, they have nothing to do with battery charging or lighting. Voltage is induced in this coil by the rotating magnets in the flywheel. This produces a pulsating voltage in phase with the passing of the magnets. One end of the coil is tied to ground and the other end is tied to the moving side of the points. From here, there is a wire to the primary side of the ignition coil, the condensor and somewhere along the way, to the kill switch. As the flywheel rotates and the current in the magneto coil is near maximum, the points open. This creates an instantaneous voltage change from 0 volts (the points had the coil grounded), to maximum voltage. This voltage change is seen by the primary of the ignition coil and induces a high voltage in the coil secondary which causes the spark. Note that this is opposite to a battery/coil ignition where the points being closed cause current flow through the coil and when they open, the collapsing field in the coil causes the spark.

If you check for all of these components and connections, and make sure the insulating washers are installed correctly where the connections are made to the points (the moving contact should only be grounded when the points are closed), you should get a spark.

For reference, the Magneto coil and the Ignition coil primary should each read about 1 ohm or less to ground, the plug wire, without the resistor cap, if you have one, should read 5 to 10 K ohms and the condensor should read infinity except for a slight kick when you first connect the meter.

Good luck,

Ron

Re: Vespa Ciao Magneto

Make sure the stop light bulb isn't burned out. Also that the stop light has a good ground. A bad stoplight will kill the ignition. If you go to Zippy's Moped Garage Forum and search under Vespa, I wrote about it this topic there.

Jim

Re: Vespa Ciao Magneto

Ron Brown /

Jim,

I remember this post now. Has anyone figured out from the wiring diagram why this happens and whether you can bypass this feature?

Ron

Re: Vespa Ciao Magneto

Okay you are going to love this one. The Vespa Ignition is grounded through the brake light system. The field voltage for the condensor is grounded throught the brake handles, when you apply the brakes you disconnect the path and the field voltage then is grounded through the brake light to ground. However if the field is not initially grounded through the brake handles you will not get any spark. This and the confusing schematic had me stumped for an afternoon while I was chasing down spark. I finally found the problem, a broken wire in my brake wiring, but I also came up with a temp fix by making another ground for the field.

I cannot recall off the Top of my head what the wire color is comeing out of the Engine that goes to the breaklights, but I can describe it. You will have one wire going straight to your coil. Another that goes to ground. And the third that connects to two blue wires, one goes to the brake light, the other will go to the handle bars. Ground it and see if you get spark. Other than that check out your coil to make sure it works. Apply and disconnet power to it and see if you get spark with each cycle.

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