Modern Vespa

I've mentioned my third scooter (how did that happen!?), Scarlett, a couple of times elsewhere, but it's time for her own thread.

Scarlett is a 1981 125 Primavera ET3 in "rosso arancio"; literally, "orange red". I bought her from Bello Moto in SF a couple of weeks ago after Hagerty paid out a total loss on Primrose, the blue 1979 ET3 I crashed in the Santa Cruz mountains back in April. Quick update there - my 23-year-old son has expressed an interest in learning to ride, helping me get Primrose to a rideable state, then taking her off my hands.

Back to Scarlett... About three days after I got her home, she developed an air leak, so I drove her back up to Bello Moto, left her there for a week for Tim, their tech, to take a look, then fetched her home.

I went out for a spin on Sunday, and I think everything's ok. The engine sounds like it might be idling a bit too quickly when it's hot, but by now I'm not sure I can trust my ears. I don't want to be driving up and down the peninsula every few days, so I'm going to try figuring things out myself...

I pulled the spark plug, and it seems good to me. If I hear clear symptoms of an air leak, it will obviously need attention, either by me or Tim at Bello Moto, but otherwise, if I regularly inspect the spark plug, am I safe to ride around?

Looks a little charred to me. Consider upjetting and a clean plug.

If you're worried can also pull the head and inspect the piston top.

If you have a stock setup you may still have an air leak.

Short term you can jet around an air leak but you'll want to find the source.

Yeah - it's bone stock. Looks like I have another drive to Bello Moto in my future

Just an informed guess. May want a second opinion from someone on here before you make the drive

Can you explain how you determined/confirmed "she developed an air leak"?

If you have an air leak, you will never jet your way out of it.

Stopping at a traffic light, and again when I got home, the engine took a while to return to idle. Ten seconds, at least. My idea was to check the plug as confirmation of whether it's still running lean, and whether that's doing any damage.

That sounds more lean than a leak to me. An air leak will have the rpm's racing like a banshee.

I.e. you come to a light and your idle is set to 1000 and you look down and it's at 1500, then you look again and it's at 2000, then 2 seconds later 3000 etc. maybe not that extreme but you get the point.

I have a Yamaha Vino that when I rebuilt had a little leak. Kicked her over and the bike went from 0 to 9900 Rpm's right off the get go.

A leak sounds probable. Do you have an air leak test gig? I would recommend taking that possibility off the table before chasing down other gremlins.

What did Tim do?
These bikes have a curious carb to manifold connection, that can introduce air and result in that delayed return.

If you just pulled the plug after a ride home, that won't tell you much.
Search "plug chop" here to see how to take a sort of picture at a fixed throttle position. A true "chop" involves actually chopping the plug to see the soot ring at the bottom of the insulator, but who wants to have to do that?

If that pic were a kind of plug chop I'd say on the rich side, but you probably rode around with the engine cooler/stop and go before pulling it.

Unless rpm is much higher and you're sure you can tell, slightly higher rpm at idle when hot isn't a sign of an air leak. Better combustion.
Like Friday said it'll race even closed throttle, and hunt for fuel.
If you pull the choke when hot at idle it should want to die without an air leak.

It's possible the mixture screw was adjusted not fully at operating temperature. In this case it could be a small adjustment and done.

Btw was this bike rebuilt in Italy?

Not sure. He wasn't around when I picked the bike up, and I haven't had a reply to the email I sent them. Thanks for the tip - I'll try that! That's what I'm hoping! Yes, Bello Moto imported it a few months ago.

Yeah - it's definitely nothing like that. I'll try adjusting the mixture and idle next time.

Tim (Bello Moto tech) got back to me. He says he removed the carburetor from the intake manifold and reattached it, making sure the hold-down clamp was correctly situated and tight, then adjusted the carburetor.

He also said that I could adjust the idle and mixture screws to suit myself as a lot of it is user preference in terms of sound and idle speed.

That, and what folks have said here, all makes sense. I'll spend a little time fettling with it until I'm happy

Thanks, all!

I went out for a ride this afternoon; when I got back I adjusted the idle screw by a quarter turn - it sounds a lot less frenetic now, and nothing like it did when it had the air leak.

I'll see how it idles when I next start it from cold.

Did the spark plug end up being okay? It does look a little charred up. Good luck!

Thanks! I haven't taken another look yet. I'll report back when I do 👍🏻

I made the mistake of gassing up Scarlett before I put her on the carrier and drove from San Jose to Santa Barbara for Vintage Vespa Days at the weekend. When I stopped for lunch after a couple of hours, I noticed gasoline running from the gas cap down the cowls. I carefully wiped it off with some napkins, but later noticed that about 1/2" of the end of the "electronic" stripe had started to lift off. Presumably the gas had dissolved the adhesive.

So - suggestions for an adhesive that will stick the vinyl stripe back down without damaging the paint?

Terry's favourite, Shoegloo

This stuff?