Modern Vespa

Hi all!

I have a new-to-me 2015 GTS Super. It's my first modern Vespa after riding a P200E for years. For the first couple weeks, it worked like a dream.

Then I rode it to work one day, left the keys in the ignition, and completely drained the battery. I tried trickle charging for a few hours and got it to turn over and stutter like it wanted to start but not quite. I then tried jump starting it off a car to no avail, so I pulled the battery and trickle charged it overnight until it was holding a charge of 13.2 volts while being charged.

After reinstalling the charged battery, it turns over the engine but I still can't get the scoot to start.

Things I've checked:

— I hear the fuel pump prime for two seconds when I turn on the ignition;
— the battery shows 12.65 volts in a resting state and about 11.4 volts under load.
— when I depress the brake and the starter, the starter motor turns over for about 10 seconds but there's no stuttering or other signs that the engine is going to start.
— when I turn on the ignition, the immobilizer light flashes once for less than a second and then stays off. (I've also tried testing reprogramming the keys with the brown master. If I only program one key, the unprogrammed key wont turn over the engine, and after the first flash the red immobilizer light stays on, whereas the immobilizer light flashes once and then stays off off if I use the programmed key, which also is able to turn over the engine. When I program both keys, they're both recognized and can turn over the engine.)
— I've tried starting the engine with the brown master key. I get the same .7 second flash, followed by quick flashes for the number of keys programmed, and then the light stays off. If I pull out the chip, then the light stays on.
— I have spark. (When I removed the plug to test it, it had a bit of carbon deposit on the side electrodes, which I cleaned off.)
— All the fuses in the glove box have continuity, which I visually inspected and tested with a multimeter.
— the Vespa has a full tank of fresh gas
— I've tried holding down the left brake handle, the right brake handle, and both brake handles while pressing the starter. Both brake handles activate the rear brake light.
— the previous owner removed the side stand. I don't believe the side stand had a safety switch on this model in any event.
— the front headlight doesn't come on when I turn on the ignition, but I'm not sure whether this is normal (and it only turns on when it starts).
— The oil light and ABS light stay on, which I think is normal since I took the battery out.

I'm at a loss here. Any ideas of what I should check next or what could be causing the issue? I can post a video of the Vespa turning over when I try to start it if that would help.

Thanks!

Sorry your new-to-you ride is giving you troubles.

I'd get a new battery before digging into anything else. That said, someone more knowledgeable than myself will chime in shortly.

How old is your battery? A trickle charger won't fully restore/charge a dead battery. However, depending on how old the battery is, it may be shot if you ran it completely dead. Might as well get a new battery.

+1 on the battery. Likely to be the culprit. Will save a lot of time and head-scratching, and worst case scenario (unless seller told you it was recently new) you'll need one anyway.

That battery isn't fully charged by any means. The boost charging voltage should be at least 14.4V, and the float voltage should be 13.6V.

The quoted 11.4V under load - what load? With the starter trying to start the bike, or just the ignition on?

As above, if it was completely drained, it's probably severely compromised now. I'd be installing a new battery as a matter of course.

Thanks all! I've ordered a new battery, which will arrive tomorrow. I'll post an update then.

I'm not totally convinced the old battery is toast, though. It's showing 12.6 volts at rest (not on a charger), which is what one would expect with an AGM battery. The voltage only drops to 11.4 volts while the starter is turning over trying to start the bike, which suggests the battery is performing okay while under load. (There's no measurable drop from 12.6 volts with the ignition on.)

While recognizing that the battery is still the most likely culprit, shouldn't it start when jumping off a car battery?

Also, should the front headlight come on when I turn the ignition on before starting the bike?

That's OK, but an AGM should be at 12.8V. Yes, so do some voltage drop tests - battery + to starter, battery - to starter while trying to start. No. Only on with the engine running and 'happy'.

My 2008 has two fuses under the seat on the left side. Not sure about your bike but you might want to take a look. I am not sure what they are for.

The new battery (YTX14-BS) arrived yesterday, and I hooked it up to the battery tender until it was fully charged before installing this evening. (The battery is taller than stock but fits fine after removing the battery float box.)

However, the Vespa still won't start. The engine cranks over solidly but there's no sign of combustion. After 2-3 attempts, I can smell the fuel, and I know it has spark.

What else should I check?

The engine needs fuel, spark, and air, and you've said nothing about the air filter. Unlikely cause IMO, but it's worthwhile checking.

The PO had the Vespa serviced at a local dealership in March 2023, within the last 200 miles. They installed a new air filter, so I really doubt that the air filter is the issue. I'll pop it open tomorrow and check. I'll also check the throttle body bypass. Do I need to pull the throttle body to do this? And do I need to use specialized throttle body cleaner or is carb cleaner okay?

What do you make of the condition of the plug? I've attached a photo showing what it looks like after cranking over the engine a few times. It's a bit hard to make out in the photo but it has a black deposit on the side electrodes. Would you check fuel injector at this point as well?

Unfortunately, the Vespa is stranded in my work parking lot, so I'm making slower progress than if it were at home with access to all my tools.

Here's a video showing the spark test: https://youtube.com/shorts/sEngi3MmWDo

And here's a video of me attempting to start the Vespa with it just cranking over: https://youtube.com/shorts/4ilyhjGqk6U

You got spark, and I suspect the original battery would have worked ok , but you did not mention how old it was and as Jim mentioned, it was probably compromised at this point. So now it's most likely down to fuel delivery. Was the Spark plug wet with fuel after you tried to start it?

Thanks! I tried to get to the bottom of the issue today but no luck. I'm totally mystified, because the bike was running perfectly until I let the battery run all the way down about 10 days ago, and I've since installed a new battery.

The fuel pump primes as expected when I turn on the ignition. In the video, I switched off the ignition after about a second to stop further fuel from spewing out.

I then tested the fuel injector while still on the bike. It's spraying gas, but does it look okay? Should it be spraying more gas?

I took the injector off, energized it with a 12V battery, and tried spraying carb cleaner through the injector to clean it. I didn't have the right size hose (1/4 inch internal diameter) to attach to the injector so I wasn't able to get as much carb cleaner through it as I would have liked. (I'll give it a better clean tomorrow now that I've sourced the correct hose.) I then reattached the injector, tried to start the bike, but there was no sign of combustion. When I pulled the plug, it didn't seem wet to me. If gas is getting to the combustion chamber, I'd expect the plug to be wetter and smell like gas. I also confirmed again that the spark is good.

I then took the injector off, sprayed starting fluid into the chamber for about 2 seconds, reattached the injector, and tried starting again. The starter cranked over but there was no sign of combustion. That's got me puzzled. I pulled the plug again and it still didn't seem wet. With the plug out, I checked basic compression by holding a finger over the spark plug hole. That seemed fine.

Out of ideas, and working in the middle of a parking lot in the sun, I moved on to air. I pulled the throttle body. It looked pretty clean, but I gave it a good dousing in throttle body cleaner anyway, letting fluid into the idle bypass hole. I also pulled the airbox, which looked very clean.

None of this helped. The bike still won't start. Here's a video of my final attempt to start the bike today.

What would you check next? Why isn't there any combustion even after spraying starting fluid into the fuel injector hole?

have you tested it with another plug?

in the spark test video, you confirm that there's spark but that looks way yellow to me. I'd be wanting to see a big fat blue spark there.

with a weak yellow spark it might be getting washed out in the cylinder under pressure.

the weak spark might be purely coincidental, but it could also be indicative of a problem with another component.

Yeah the spark did not look good and I can definitely see it being non existent under pressure. The strange thing is why isn't the plug soaked with fuel? FI will shut down the fuel pump (or not start it) after a short period of cranking if it does not see a reasonable RPM signal when starting, one of the reasons for the pump prime. Does the FI Piaggio uses do this, I have no idea (it should, raw fuel in a cat is not good). Starting fluid, not recommended, should have did something so focus on spark.

The starter fluid should have made a couple of pops at the least. I was going to suggest using some of the fluid, but it's really a last resort. Anyhow, unless the compression went south or the decompression lever has gone wonky, you should circle back around to spark as others have suggested. Start at the spark plug, maybe replace with an Iridium one and look at the spark plug cap. If at all suspect, try a new one - I like NGK caps personally. Then check for spark again. Then report back.

Thanks for all the suggestions! I cleaned out the fuel injector again, spraying through a good amount of carb cleaner. (1/4 in ID tubing secured with a zip tie to a can of dust off is a good solution if you don't have access to a compressor and rubber tip nozzle.)

I then recharged the new battery overnight, as I'd cranked over the motor many times over the past couple of weeks, and swapped out the spark plug. Started up first time!

Greasy, good to see you're still kicking around these parts! You ported the piston and installed the bearings for my P200 rebuild back in the day.

Glad it worked out. The spark plug you showed a pic of with the double side ground electrodes is a bit of a gimmicky thing, the iridiums are really the way to go. They can take the most punishment and keep going. Install with some copper slip on the threads and it will outlast your love for the scoot.

glad to hear you got it sorted out man!

still kicking around, still building bikes! holler if you ever need anything!