12v DC Wassel Stator Plate Fault Finding?

[Donnie]

Right, hating electrics as i do I want to suss out how to check the stator plate on my wassel conversion as I've had issues on the way and back from the IOW this weekend. I seem to have eliminated everything else at this point

So, all I need to suss out is how to check the earths and pick up and coil, I know its usually earth wire to mag housing, then earth to pick up wire then earth to coil wire BUT on a DC place the earths been desoldered then an extra wire run up to the wassel regulator.

So, Im thinking

a) check the ends of the 2 earth wires to ensure theres a short circuit there. then connect one of those to an earthing point on the engine or frame.
b) continue to check red and green off the stator as per normal?

[coaster]

The only earth wire that is disconnected is the one from one end of the lighting coils and that is so that the 2nd yellow can be attached to the coil. All other earths should be attached to the stator. Attach your meter on resistance to the white wire and an earth on the engine, you should get very close to a short circuit. Then move the earth lead to an earth point on the frame and you should get the same reading. If you don’t then you need to check the engine to frame earth is sound, i.e. no rust or paint preventing a good contact.
The most likely cause of a poor earth is the rivets on the stator core that hold the earth tags, these often work loos and need a tap with a hammer to make them tight. This will require the stator to be removed and the rear of the rivet supported on some solid still (an anvil or bench vice) whilst the outer end is peened with a ball peen hammer.
What were your issues with the stator?

[Donnie]

Cheers mate That makes sense.

On the way to the IOW friday I had hassles, we'd stopped for petrol, about 40 miles from portsmouth and she just wouldnt start (we'd been stopped for about 40 minutes due to another lad having issues. Anyway, it was like it wouldn't start, wouldnt even try.

Checked plug and for loose wires, checked Id not inadvertantly flooded it and it started after about 5 or 6 kicks. Usually starts first time.
Anyway, a mile down the road, it died, completely cut out, just like fuel starvation. Hoping a quick repeat of earlier would sort it at the side of the a34, I soon waved the others on as it was obviously not to be.

Anyway, long story short, pushed it off to a slip road, tried changing and checking all the usual suspects and rang recovery, after 2 hours waiting and another call to them to be told another hour, I had a basil fawlty moment and kicked and swore at the scooter, then kicked the kickstart and it started!!!!

Was fine then all weekend until 5 miles from home yesterday when it did the exact same thing! Im planning to check stator first as if its the regulator im buggered as I don't have a spare wassel regulator at the moment. Only a standard one.

[rosscla]

Your regulator and lighting circuit are completely separate from the ignition circuit, assuming there's not any shorts. So it's unlikely to be anything to do with your regulator.

First I'd check by taking off the green to the ignition switch from the cdi, then check the resistance to earth as coaster suggested, then change the CDI for a known good one.

Was it wet at all? Where is your CDI mounted? Are the contacts on the CDI exposed or covered by a rubber boot?

[Donnie]

already changed cdi for a known good one, not mine though so I must get a spare. but yeah cdi is mounted up on the footboard leg and I have all connectors covered with individual covers. It was dry as a bone when it happened first time, but was wet as hell on the way back. same symptoms both times.

[coaster]

Rossclark is correct, there is absolutely no connection between the lighting and ignition. Personally I doubt if it is the CDI, I have had several CDI's fail on me over the years and they have always died completely, either whilst the scoot was still running or just by refusing to start after running fine. I would hazard a guess that the LT coil has a break in the wire which is only just making most of the time and is breaking down intermittently. I've had this a couple of times, the last time I proved it by connecting the meter on ohms between earth and the green wire which initially gave me a healthy reading but then I started tapping the coil with a small piece of wood (needs to be non-conductive) and noticed the reading jumping. Gently prizing the paper insulation from the coil revealed a break in the very fine wire before it joined to the green wire. It could also be poor crimping on the stator leads or a poor earth between the engine and frame. The pickup might also be at fault but I think they are of a solid state nature so not as prone to failure as the LT coil.

[Donnie]

Yep, cheers for all this lads, hoping to get it on my bench this afternoon and start checking the stator, good trick re the tapping of the lt coil there coaster, I'll have to check that.

[coaster]

Yep, cheers for all this lads, hoping to get it on my bench this afternoon and start checking the stator, good trick re the tapping of the lt coil there coaster, I'll have to check that.

Just make sore you don't use anything metallic as that will generate a small current and mask your readings

[rosscla]

I agree the most likely cause is the LT or the pickup.

However the reason I asked about the wet is this used to be a typical issue on vethpas when I ran them in the 80s. The positioning of the coil near the rear wheel, particularly if the back end was cut or the panels off, would lead to the CDI getting wet and causing intermittent cut outs. This often occurred if the top of the unit was cracked. You always used to carry a can of wd40 and a good dowsing would often get it going again.

The CDIs in use are similar or interchangeable with the Vethpa item and I thought it possible it could suffer from a similar symptom? On the Vethpa they have a rubber boot protecting the connections which is rarely fitted on any Lambretta application I've seen. I'm also of the opinion that the reason that a lot do CDIs fail completely is that they're simply shaken to bits inside due to being bolted directly to the frame in most Lambrettas. I'm now rubber mounting mine and we'll see how it goes.

[coaster]

.... I'm also of the opinion that the reason that a lot do CDIs fail completely is that they're simply shaken to bits inside due to being bolted directly to the frame in most Lambrettas. I'm now rubber mounting mine and we'll see how it goes.

Same here, mine's mounted via 2 exhaust bobbins and apart from a spate of 4 blown CDI's (2 Indian and 2 Ducati's) due to an electrical fault I have never had a CDI fail. That's thousands of miles on cheap as chips £9.99 ebay cdi's. I have a ducati on now but that was only bought because of the Euro in Switzerland this year.