Modern Vespa

Finally I have everything together and am trying to start my 1974 Primavera. I had the engine out to replace seals after sitting for the better part of . . . 15 years. I took the time to build a new wiring harness and convert to 12 volt. I specifically set up new the wires to the junction box to match the VAPE diagram so there would be no guesswork. I was pretty meticulous with the harness and all of the accessories work.

Fuel, compression, spark. I have 2 out of 3.

Yes, I did kick loose the spark plug wire, how did you guess? But I fixed it and checked for continuity between the CDI end of the wire and the cap. Once it's connected on the CDI I can't see a way to verify that it is screwed in to the CDI properly. (I made a little mark on the wire to see that it went in deep enough because it's a bit of a PITA.)

I went over the kill switch wire to make sure I have that set up right. The wire itself has continuity which is broken when the switch is in the "on" position.

Is there anything else I can check to eliminate or not the CDI? I know there are other posts on troubleshooting ignitions but I didn't see my situation there quite -- so thanks in advance.

Is the CDI's metal bracket grounded to the frame?
Is the regulator grounded to the frame?
Is the engine block grounded to the frame?

90% of all electrical issues are caused by a bad ground.

Brown needs to be grounded to CDI bracket and CDI bracket also to engine…

This is how I have mine…

1. Yes.
2. Yes.
3. I don't have any additional ground wires but it is bolted into the frame.

I have the brown wire from the stator grounding to the CDI bracket, and since I was a little worried about the rubber bits I added a second wire grounding the CDI to the bracket. You'll probably recognize the screen grab. I didn't want to pay an extra $16 for bolts and grommets, so I got stuff from the hardware store. I was worried that the grommets were isolating the CDI from the bracket.

Also just now, to double check, I ran a jump wire from the bracket to a ground. No change.

Is that black wire on the fan shroud screw the one you mean?

My setup.

Yes, I put an extra wire connected also to brown since the main bracket is on rubber. Have you tried without the kill wire connected??

+1 on everything already suggested.

Next, isolate the ignition. Disconnect the kill switch and AC out from the stator. Connect only the red and white wires to the CDI. Mount the CDI to the motor, of course.

Get a new spark plug to test with and verify you (don't) have spark when it's grounded to the motor. Bonus points for testing this without the plug in the motor so it spins better.

Assuming that doesn't get it, pull the flywheel and make sure the stator is seated properly. The vape's trigger is really sensitive to misalignment.

Past that, maybe the CDI really is bad.

I like that solution. I think I'm grounded now but when I take out the CDI next I am going to do that.

I have not tried without the kill wire connected. I may have to wait until tomorrow, but I will report back.

(big snip) Thanks for the to do list. I will report back.

FYI, the rubber insulators in the CDI mounting bracket make really good insulators. So do the upper and lower rear shock mounts, so do the rubber engine mounts. Ground (earth) redundancy is a good thing!

Thanks for the advice everyone. I went out to the garage, disconnected the kill switch, and it literally started on first kick. Video below is 3rd kick.

Now I can get on with the next steps.

That's outstanding news!

Yeah, there's a reason that I *always* tell people to isolate electrical issues as much as possible when troubleshooting, and you just experienced it.

Clear and methodical thinking and a little distance help a lot. Thanks.

Got a chance to get out to the garage to figure out what I did wrong, so I'm putting it here to document one more way of screwing things up, hopefully to spare someone else. When I put the headset on, I thought I had the new harness in its sheath clear of the headset bolt, but I did not, and tightened the bolt right down, smashing the sheath and the kill wire and grounding it out.

In my defense, it was probably cold and dark, and I was probably tired and frustrated with getting all the headset bits lined up.

It's going to be annoying taking the headset off, but at least I can get to the fault to fix it.