Modern Vespa

Hi all
I have a 63 sportique with a 177 kit and px ignition
I keep burning out stators every time I push the engine hard
I would have thought if the engine is getting that hot it would have seized before cooking the stator
Any ideas folks

Sounds like the voltage regulator is buggered, voltage going too high when revs are up.

Hi how would that work doesn't the stator generate power and send it to the voltage regulator?
Do you think the regulator is pushing voltage back to the stator causing it to burn out ?

The stator voltage (with no regulator) will rise with revs, I've seen 40 volts before.
The regulator takes that voltage and dumps it to ground (although they don't all work like that), at least that's my understanding.

So if your regulator is not working and allows the stator voltage to rise too high then possibly that is your problem. However thinking about it now then your lights would be the first to go. So maybe that's not the issue. But check the voltage anyway to see what it does.

If it's happening to different stators then perhaps you have a short somewhere to the frame. As you speed up the amperage produced increases beyond the stator's safe limit. Worth disconnecting the stator and going over the wiring testing for shorts.

Check the flywheel and or crankshaft, if the flywheel isn't torqued correctly, it can wobble creating vibrations or arcing that damages the stator. Also, excessive axial or radial movement could misalign the stator and rotor.

What exactly do you mean by "burning out stators"?

Is your CDI grounded?

I'm on my 3rd new stator they last about hundred miles if I push the engine hard it seems to damage the stator I put on a new one and it's fine for a while

I fitted a new Ducati CDI and have grounded on the spare green wire

Spare green wire?
Blue Ducati CDIs have yellow ground wire which must be grounded to the crankcase.

Like yours it's grounded to the the screw holding on the flywheel cover
It might be yellow 😬

You replaced the stator and the CDI, maybe the issue comes from the regulator ? Is your wiring loom in good shape ? No cooked or crunchy wire insulation ?

I will replace the regulator and hope that solves it because being a old Vespa the loom is tucked away inside the frame proper nightmare to get at I think

I'm not getting this. I do not understand what you mean by " burning out stators". You have not, as far as I can tell, described the actual issue.

The stator coils provide power to the lights, horn, brake light and CDI. The single ignition coil feeds the CDI on green and the other green goes to the kill switch. The red is from the small black trigger coil (basically does what points do) and white is grounded at the stator. The CDI power is not connected to the regulator and is unrelated to the other coils. If the regulator is bad and does not restrict power, the bulbs would blow out. Replacing entire stators with no remedy to the problem is a waste of money.

As Ginch stated : "If it's happening to different stators then perhaps you have a short somewhere to the frame. As you speed up the amperage produced increases beyond the stator's safe limit. Worth disconnecting the stator and going over the wiring testing for shorts. "

Moto's right. There's some confusion about what your problem is.

Stators themselves don't "burn out".

Stators have coils mounted on them.

One coil is for the ignition. The others supply current for the lights, horn and/or recharge the battery (if you have one).

Which coil is giving you trouble?

Do your stators look like this?

Stator looks like photo
I think it must be a short?? as my lights are not blowing the problem is ignition
I assume the ignition coil is getting damaged causing the scooter to stop running then will start again but run for a short time
It's not fuel problem as that's been ruled out
It's cured for a time by replacing with a good stator until that fails
How do I test the wire loom for shorts ?

The small black box is the trigger and the one with the yellow tape is the power for the CDI. For about $25 you can just replace this feeder coil. The other four have nothing to do with ignition. The fact that it runs at all indicates to me that the coil's probably fine.

When it craps out, have you checked the plug to see if it's firing? Hold the body of the plug against a ground and kick the motor over to see if it's sparking. It is also possible to have a bad plug. Is it wet or dry when this happens? Could also be a fuel flow issue when you push it hard as you said? Also, when it dies does it start back up?

You should be able to tell which of the green wires at the CDI is coming from the stator and which is connected to the harness at the junction box. The sheath colors are probably slightly different and one will be coming from the case and one will be going through to the harness. This is the kill wire that is shorted at the HB switch to kill the ignition. Disconnect the one to the harness and see what happens. You can kill the motor if it runs by putting it in gear and stalling it with the brakes on.

Good idea of Moto64 to look at the plug. A few years ago I did a long day ride with some mates to go camping. Up until about lunchtime mine ran perfectly. Then it began to stop randomly... must have stopped at least 20 times that day. I tried a new plug and it started straight away. That was my only spare plug so I stopped at a bike shop and bought half a dozen. Eventually we got to where we were going and while my mates went to get beers I started pulling stuff apart to see if I could find anything. I did find it eventually - I had trapped the fuel hose between the cylinder and cowl and it was barely getting through and evaporating. Changing the plug was just enough time for the cylinder to cool a bit and fuel to flow again.

Get your multi meter and sharpen one of the probes. Poke the wires with one and hold the other to a good clean ground on the frame and look for continuity on all but grounded wires.

You can also test your stators to make sure it really is fried. Somewhere here there is a thread called "Stator values wiki" or something like that. It's pretty easy to test, have a look for it.

The more I think about this the more I think it is fuel related. If the motor starts and runs until you " push it hard" it has to be fuel. The ignition doesn't care if you're pushing it or not. In fact, you rev it harder in the first three gears than in fourth. Plugged breather hole in gas cap? Too long or kinked fuel line? Plugged screen on tap in tank or under cap on carb?

You can disconnect all the wires in the junction box and the green kill wire at the CDI and it should run just fine with the red, green, and white from the stator connected to the CDI. Swapping out the stator plate with a new feeder and trigger coil pretty much rules out any issues there.

Tell us how this occurs. You start it up and ride it a while than you "push it hard" and it just dies? How far do you get and it is always the same? Full tank or low on reserve?

When it craps out, have you checked the plug to see if it's firing? Hold the body of the plug against a ground and kick the motor over to see if it's sparking. It is also possible to have a bad plug. Is it wet or dry when this happens? Could also be a fuel flow issue when you push it hard as you said? Also, when it dies does it start back up?

You should be able to tell which of the green wires at the CDI is coming from the stator and which is connected to the harness at the junction box. The sheath colors are probably slightly different and one will be coming from the case and one will be going through to the harness. This is the kill wire that is shorted at the HB switch to kill the ignition. Disconnect the one to the harness and see what happens. You can kill the motor if it runs by putting it in gear and stalling it with the brakes on.Ml
So plug is sparking fine and there isn't a fuel flow issues I've run it will the green kill wire disconnected and makes no difference
I have replaced the pick up and power to coil modules on the stator on one stator it worked fine for 100 miles then when pushed the engine it failed again
Yes the engine restarts after it stalls but each time it stalls quickly after a few mins riding once the initial stall happens
I know it sounds like fuel issues but I've tried a different carb and I've removed the tank to check for any pinches it's defo not fuel
The only thing that resolves it short term is replacement stator or soldering in new modules I'm not source if it's the pick up or power to cdi that's failing
How can I test that ?

You said you replaced the CDI so that's not likely the issue.
Set multi meter to Ohms (resistance) and connect to green and white wires disconnect from CDI. What do you get? Also red to white.

Stalling and then restarting after a moment and then stalling again sounds like a plugged breather hole in cap. Try with cap loose? The fuller the tank, the sooner it forms a vacuum and stalls.

Also, what do you mean by " pushing it hard"?

So it runs fine for a few days probably around 60-100 miles 4-5 outings gentle and pushing hard on dual carriageways then the problem occurs usually after a sustained full throttle run on dual carriage way for 5 miles or so coming off the throttle it will start to stall then start up again and stall after 5 mins getting progressively worse even if I give it time to cool down
Hope that helps a bit as mentioned fuel problems have been ruled out it will start easily right away after stalling but just won't keep running

I've even tried it with the fuel cap off that was my first thought

One more question : when it stalls does it just quit or does it die like it's running out of gas? There is a distinct difference. What plug are you running? Next time when it stalls immediately pull the plug and see if it's wet or dry. Other than that I am afraid I am out of ideas.

Couldn't that be soft seizures ?

Possible , I guess, but it's odd that it does it over and over again. You'd also feel it in the rear wheel.
I'd pull the plug immediately after it stalls. If it's wet the ignition quit and if it's dry the fuel ran out.

I would put a temp sensor on the cylinder head or under the plug and check when the shit happens

It's wet 😬

I have a temp sensor on my dig speedo wire to the plug what temp would be too hot ?

Stator readings ohm set at 2000
Stator 1 green to E 468, green to red 578 red to E 111
Stator 2 green to E 510 red to green 622 red to E113
Stator 3 green to E513 green to red 608 red to E 96
Are they ok or knackard what should the readings be ?

I'm guessing the pickup (aka the black square thing) is loose, worn, misaligned or has a bad connection.

On all 3 stators ?

Stator Values Wiki

They look pretty close compared to the wiki except for the last one.

I keep thinking (assuming fuel is absolutely a red herring) that there is a leak to earth somewhere. Perhaps try the power wires at the junction box - blue and black I think?? Without the stator connected. Might need to bounce up and down on the seat or something.

I guess you could check the flywheel and look for signs of arcing or at least touching?

Does this have a battery?

The one you posted a pic of looks pretty worn. When was it replaced?

Can't wait for the resolution of this one. I keep thinking that CDIs have been known to act up.

That's actually a very good point! I've known a CDI to fry a stator on my own kit before now...

Can you replace both and feedback the results?

Maybe try another one? Is the one you put on a real honest to goodness Ducati ? Can you borrow a known good one from somebody? After three feeder coils and triggers it seems more likely that something is preventing the plug from sparking more than not providing the power to do so.

Edit: I just re-read your line and question grounding on the "spare" green wire? One is from the feeder coil and the other to the kill switch.

No battery
I tried running it with just the ignition red green white but probably the stator damage was already done 😬

The one in the picture is the original piagio one
I really have tried everything except pulling the wire loom to see if it's earthing somewhere
The cdi is genuine Ducati when problem first occurred I took into TASS and the stator and CDI were replaced