Modern Vespa

Ciao, Vespisti!

Over the past week, I've noticed my scooter's power has been a bit lower than usual. I usually reach 43–45 mph, but lately, I'm maxing out around 38–40. The last few days, I've also noticed a slight "chugging" feeling, like there might be too much air in the system.

Today, I got about five blocks from home before the scooter died. Thankfully, thanks to all the great advice from this group, I now know my way around under the pet carrier, so I took a look.

It turns out my airbox is just sort of hanging loosely inside the body—it seems like it's supposed to be attached to something that's no longer there. Because of this, the intake hose had disconnected. I reattached it, but the scooter still won't start.

I checked over the engine, and everything else seems fine. The engine turns over, but it won't catch, and the kickstart didn't help either.

Any ideas on what to try next? 😅

It sounds to me like.. no spark or no fuel.
Combustion just needs, fuel, air and a spark.. in right ratios, of course. 🤪
I think it has one of those pressure-driven fuel taps… with 2 lines.

One hose pulls from carb pressure to pump fuel through the other.
If the diaphragm inside has failed, it wont blow fuel.
Disconnect the fuel line from the tap and crank it over. It should squirt gas. If it doesnt…the tap is suspect or its not getting the pressure from the carb/piston cycle.
Replace that line and remove the other one from the tap, put your thumb over the end and crank it over. You should feel air pressure.

https://modernvespa.com/forum/topic187746

If not..possibly shot rings? 2 stroke, right?

Gradual loss of power then no run? Hmmmm.
Could be as simple as…or more.
Check the fuel tap/delivery first.

Awesome — thank you for your help and for the linked thread with diagram! I will give that a try. 🤞🫶

I am having similar problems and my local dealer told me that it is definitely the reed valve, partly because I've already replaced CDI, Carb, lines, plug and air filter. Reed valve prevents blowback and sits just under the intake manifold. I'm replacing the manifold as well just to ensure good vac. Haven't gotten parts yet, but they swear that's the problem. Maybe check that?

I'm pretty sure it's not the reed valve or intake, as I replaced the intake manifold and cleaned the carb a few months ago.

At this point, I feel fairly confident that the issue is vacuum-related, as I am able to pull fuel while sucking on the vacuum tube. Connections, seals, and gaskets all look good, from petcock joints to carb joints to air box to intake.

I sprayed carb cleaner over the joints as the engine turned over and didn't notice anything useful. Holding down the start and letting it turn over for an extended period isn't helping, but occasionally the engine almost catches and the headlight comes on briefly.

Repeatedly killing the battery while trying to start up is really cramping my style, though, haha. I keep having to charge and try again.

I'm not sure what to try next and would love any suggestions or advice! Thanks so much! 🫶☺️

Rent-borrowing a compression gauge from a friend or auto parts store is probably in order.

Well, folks are still trying to help me with another of mine…so I'll keep thinking about yours.
Here's a link to a manual.. just in case.
https://www.manualslib.com/manual/1356876/Vespa-Et2-50.html

Not being able to see or hear it… it turns over..makes compression, has fuel to the carb, at least…
Does the spark plug get wet..indicating its getting fuel, just not igniting. After cranking it, pull it and look.
I dont know what the airbox looks like..but theres not a loose snorkle or something?
I have a 49cc minarelli also and its not difficult for the airbox to dislodge..and too much extra air will make it too lean. I think they're already lean, for EPA.
Also, can you put a thumb over the spark plug hole and turn it over. It should at least pop your thumb off, as a seat of the pants compression test.

Seconded on the compression check.