Modern Vespa

I am having a problem starting my ET4 (as described elsewhere). It was suggested that I test, and/or may have to replace the voltage regulator. It is my, perhaps faulty, understanding that the regulator only comes into play when the engine is running...which mine is not. I am not getting any spark, as revealed by this method -- with the coil connected to the CDI, and an extra spark plug inserted into the cap (which is good) and placed in contact with some metal on the scooter. Nuthin'

So, could the voltage regulator have anything to do with this?

I would guess it's more likely that you'll have to replace your CDI, if spark is your problem.

Your regulator / rectifier is more involved with your electrical items - horn, electric start, lights, and keeping your battery charged.

-Eric

Can't say about the ET4; but on the GTS, the regulator is a rectifier as well - it rectifies the 3-phase AC from the alternator, and regulates the resulting DC voltage. At idle rpm, the alternator has a lower output voltage than the battery, so the electrical system runs on battery. At higher rpm the alternator has a higher output voltage than the battery - and has to be regulated so as not to overcharge the battery or over-drive the accessories. So, yes, you are right - the regulator only functions while the engine is running.

I'd guess it's the CDI as well. Could also be the spark plug lead - high voltage will arc to chassis through cracked or broken insulation.

Just to be sure because it was left out of your detailed description, you did have the key on, kill switch to run, brake lever pulled in and electric start turning? Just touching it to something metal will not make it spark. It has to be trying to start with all the process moving as normal. I just ask because it wouldn't be the first time someone innocently misunderstood directions on how to test for spark.

i had starting issues too and i had to get my coil on cdi for my et4 replaced at 7k. part was cheap though i think it was $26 retail.

Yes to all the prereqs mentioned above. I also replaced the coil and spark plug. And the Vespa shop double checked my coil and cap/wire and plug. It got spark on their ET4. I think, based on the consensus here, I can eliminate the regulator as the problem . Everything seems to point back to the CDI . The odd thing is that the indicator light emits an "okay to start" signal. Mentioned elsewhere on this board (for a starting problem with similar symptoms) was the advice to check the CDI to ground connection. All the connections I can find look fine, clean and secure. Here, I may have missed something. If anyone can point out the places the CDI connects to ground that I should be checking, that would be great. For a more complete account of the situation, you can see this other post ET4 Resurrection - Help

Check your grounds. if a neg wire is grounding out, it will cause what you speak of.

You said NO SPARK --

I am working off of page 11 from the tech manual available in the Tech Library and generic knowledge/experience with ignition systems.

Check 12 V feed to CDI. This is at terminals 4 (red/blue) and 5 (white/red). 4 should show 12V at all times, 5 only when the ignition switch is on. If there is not 12V here, then you have a regulator problem or bad wire(s) from the regulator to the CDI. I doubt this, as you say the CDI LED is working.

Check the spark plug wire for continuity.

You said somewhere that your coil works on another scooter, so we will assume it is OK.

There should be two leads going to the HT coil from the CDI. One is purple, the other is black.

The black lead should show a good path to ground. at both the Coil and CDI. If not, check for the location of the break.

Check the purple lead (disconnect at both ends) for continuity. If it is "open" then find break and fix/replace.

If purple lead is good, check to see if the Purple lead to the coil shows 12V blips as you crank over the motor. If it is not, then the CDI OR the ignition pickup at the stator are suspect.

I would check the ignition pickup first. Check for proper ground and check the green wire from the CDI to the ignition pickup for continuity. If the ground and green wires are OK, then you should check the ignition pickup itself. I'm not sure exactly how this component is fully tested, but the following can identify one type of failure: With everything turned off, and the green wire disconnected, the terminal on the pickup should NOT show a path to ground..

There is also a part on the stator that triggers this pickup (not sure what its proper name is - old age and memory).

If you aren't getting the required "pulse" to ground from the pickup back to the CDI, then there will be no spark. And that's a combination of the electrical function of the pickup and the device that triggers it. Either or both could be at fault.

If all of the above check out OK, then the only item left in the system for spark is the CDI.

Hope the above helps.

Good Luck. Let us know what you find out.

Al

Have you checked the stators output?

Ive not had many CDI units fail, you do get the odd one, and normally its an immobilizer issue and they dont retain the key code and give the constant LED light....

Before you replace a CDI double check the stator is giving the CDI its trigger to fire

cheeky_

How do you check the trigger device? It provides a momentary path to ground to the CDI. Will a continuity tester catch such a short duration pulse? I know you can test it to see if it's shorted out, but I just have never had occasion or advice on how to check to see if it "closes" the circuit. The duration is in the microseconds range. And, there is the magnetic part that activates the trigger to check as well.

Al

Thanks all! I think I've checked most of these things once or a million times. And will do so again and report back. One "not as specified" read I recall involves the HV coil, but I am not sure it is of much significance. At the control unit, I checked the HV coil terminals. There is continuity between 3 (purple) and 8 (black). The resistance here is supposed to be 0.4-0.5, but it is 0.9-1.0. Repeat the check directly on the +/- terminals of the coil itself, same read. Which is why I replaced the coil in the first place (turns out the one I replaced wasn't bad after all). And the purple lead (disconnected at both ends) does show continuity, as does the black (fairly high resistance on the black as I recall though). Aviator47 noted that "The black lead should show a good path to ground at both the Coil and CDI." Does this mean that the black wire should not produce a read at all (when connected, meaning not just from end to end on the segment that exists between the CDI and coil)? I can test all sorts of connections - sorry, but I don't yet have a really good grasp of the big picture of how all these things work together to make spark! Thanks for your patience and assistance! I will add more info as it becomes available for your puzzle-solving pleasure...

"The black lead should show a good path to ground at both the Coil and CDI." Does this mean that the black wire should not produce a read at all (when connected, meaning not just from end to end on the segment that exists between the CDI and coil)?


According to the Vespa manual, the black lead from the CDI to the coil should be grounded. I am not sure where that grounding connection is made. Disconnect both ends and check resistance from each end to ground. Should be zero. And, unless there is something involved that I cannot see, if you disconnect both ends (CDI & Coil) and check resistance across those two ends, it should also be zero.

The more I think about it, the more I suspect the ignition pickup at the stator, its wiring back to the CDI or to ground, or the magnet that actuates it. That's what triggers the current from the CDI to the coil to get a spark.

Realize that I am working strictly off the wiring diagram. Have never played with a LEADER engine.

PM me and I'll write as detailed a description of the ignition circuit's operation as I possibly can. If you want.

Al