Modern Vespa

This scoot is acting funny.
Riding normal, out of nowhere- all power loss, like if you turned off the key.
no bumps or potholes to jiggle any loose wiring.
It just cuts out.

coast to a stop, key still on, squeeze brake, restart the scoot. it keeps doing this all the time now.

Scoot runs perfect until it just dies.
It does not have a sidestand kill switch.

parts changed or inspected:

new battery
new injector
power relay block
all fuses are good.
new spark plug-- cap is on tight.

while its running normal, I jiggle the key and push all the buttons. try to recreate it---nope, nothing makes it die.

but it just does it on its own, no warning.

im thinking a bad coil or coil to plug wire. sporatic continuity ????

what do you guys think? Help

Dodgy kill switch is my first thought

I thought that as well.

I beat on it and shake it while running, cant recreate the effect.
Maybe I could disassemble the switch and rehab the contact points inside.
worth a shot.

My Goldwing start switch did the same thing in killing my headlights.
The electrical grease that Honda puts in their switches gummed up the little brass contacts.

frustrating !!!

While you say you did not hit any bumps, it could be related to the movement of the scooter.

While you say the plug cap is on tight, is the wire twisted in tight on the cap? The cap is just twisted onto the plug and the wire does not have a lot of slack

Also, may be a contributing cause, what is the rear shocks preload set to? Unless the dealer or you changed it, it is probably set to the lowest which allows for lots of movement.

Please bear with me - are you saying that just the engine dies out or all power dies out - as the dash, lights, everything goes out?

dash is still on. I can even restart it while coasting. it instantly restarts like nothing happened.

so, possible power relay glitch/ voltage drop or ECM hiccup.

i dont know which rabbit to chase.

I'll redo the spark plug cap to rule it out.

the stock shocks are set to 4. stiff but plush. very little movement.

Check the coil end of the HT lead as well.

Also, check the 'injection loads relay' - on the left-hand side under the pet carrier - and fuse no.3 connections.

I swapped that relay with my 09 250 relay. still does it.

my hands barely fit for access to the spark plug.
the coil wire is alot harder going thru the hole behind the battery. I can get 2 fingers in there. without pulling the floorboard off, cant confirm the wire lead is seated to the coil.

no. 3- 10 amp fuze is good. wires leading to it are solid, fully connected.

are Vespas finicky to only run a certain type of sparkplug ?
kinda like my mower, it only runs on a Champion. No NGK's allowed.

this is all good advise tho. thankyou for your input to help me fix it.

So, just an electrical/ignition snafu. I'm sure you have done this but I would start at the battery, work towards ECU, the coil, the wire, cap and lastly the plug. You are looking for loose connections or a spot where the wire has rubbed the insulation off and is grounding out. I have no love for Champion plugs, but unless it doesn't look good, I don't think that is you problem as you can start it up again so easily. This is an electrical interruption so the kill or ignition switch is also suspect. I haven't taken the kill switch apart to check out for corroded contacts before, but I'm guessing it is possible to clean up. You may want to bypass it as an experiment to see if that eliminates the problem. Do you have the ignition key on a ring with a bunch of other keys? That plays hell with the switch, I'm told. Don't give up, you'll get this.

I like NGK and Denso, never had a problem with either. I have had problems with Autolite, Champions, Bosch, etc.. The only machines I know that like Champions are lawn mowers and Harleys.
I feel your pain here, that's why I install Iridium plugs as they will last a very long time so I don't have to get back in there anytime soon. The plug gets a little copper slip in the threads and silicone grease on the inside rubber boot just in case I need to remove it someday. My knuckles are torn up enough.

did you check the fuse with eye balls or multimeter?

eyeballs. the fuse is seethru, not the euro plastic housing kind.

I have heard stories of fuses that look fine but are toast on the inside.
how is it that the scoot runs great until it just dips out and then continuity is restored.
thats what is puzzling, there has to be a break in the closed loop circuitry.

im gonna inspect and if needed replace the coil wire.

the plug cap as well.

If I can replicate the issue on the centerstand, I'll do it at night, then I could see if theres an electrical arc leak jumping out the wire sheath.

I doubt it's the fuse itself - they tend to remain open circuit once there's the smallest break. They're just very dim lightbulbs after all, and they can age out without visually appearing to be broken. So they have to be measured with a meter to be certain. However, in your case it wouldn't have mended itself, so let's chase down the more logical culprits.

Don't just check the positive feeds - check the grounding too!

https://manuals.wotmeworry.org.uk/Vespa/GTS250/

no meter to check the fuse, ok swap the fuse into another circuit and if that circuit is good the fuse is good

It sounds like a bad coil. Pull lightly on the spark plug cable. If you find yourself looking at the end of it, you found your problem. This does sound like what coils do when they get old and start to go bad. And, just so you know, it's not fun to change one.

Update !!!!!

New symptom showed up on the way home. It had a higher than normal idle. Also sometimes eratic, up\down idle as well.

I have not had a chance to start poking around at it.
I hope to have some time Saturday to tear it apart.

Update again.
tore apart the floorboard to gain access and remove the coil.
clean the terminal 2 wire input contacts, confirm the plug clicked in seated.
confirmed the lead wire seated as well.
inspected the spark plug wire, no rubs, melted spots or obvious cuts in the sheath.
Plug cap is solid and lead wire screwed in tight.
green insulator boot is still good.
pulled the intake to clean the bypass idle hole, just for kicks.
replaced the no.3 fuse.
The main 4 pole power relay on the right side wall has no hot spots.
cleaned the contacts for the positive and negative leads on the starter.
confirmed the new battery has 12.8 volts while at rest and 14 while running.
No obvious frays or hot melted spots in the main wiring harness that I can see.
The induction load relay was swapped from my 09, its confirmed good.

The key ring has only the blue key and the trunk key on it. Not a weight issue for the ignition switch jiggling.

Went for a 10 mile runaround tonite.

NO CHANGE!!!!!!
It still dies but the dash is still on showing power.
It cutout several times, then it come back.

Tomorrow I will try again.

At this point, after all the work you have put into it I can only suggest that you by pass the kill switch. If that does not work, I would have to agree with Motovista and replace the coil. Meanwhile, good for you getting your hands dirty and putting in the work.

I would suggest you order this coil wire with cap attached. SKU CM083306 from Scooterwest

Quick extra question - does the cutting out happen at all before the engine has warmed up? Twice in my life I've had coils that were temperature sensitive - one was open circuit before it was warmed up, the other intermittent when it got hot. The first had a work-around - ensure the points were closed and leave the ignition on for a minute, that warmed up the coil! The other needed a new coil.

Not really, it does it at all times. 2hrs running or 2minutes.

I thought that could be an issue as well. I had a Honda Civic 4 banger that had individual coil packs. No.2 coil would start cutting out and triggering a misfire if it ever warmer than usual. Never did it while cold.

Problem solved !!!!!!

I removed the kill switch, dismantled it, full rehab on the contacts.
Went for a 60 mile ride, perfect.
You and Tierney were right the entire time.
Kinda feel naive for not going that route first. I should've done that last week.

Thank you everyone for their help.
I'll pay it forward if the same issue comes up on here again.

I'm gonna go ride.

Good man for hanging in there and sorting it out.