Modern Vespa

While riding yesterday in 3rd gear, my 76 Sprint Veloce w a 177 kit simultaneously lost power and stalled. I pulled over. I found that the motor had not seized, but when pushing the flywheel by hand, the motor has less compression and the kick start is not connecting when trying to start it. It does ratchet back though.
I was thinking maybe soft seize or something else. Any ideas?

Stock clutch?
Rotating the flywheel feels like less compression without clutch resistance.
Clutch bell expands and releases the retaining ring.

Embrague = clutch here:

*Chiavetta = Woodruff key

Certainly could be the clutch. The 76 Sprint V had a six spring clutch stock, so if you have a decent/modern kit on it, you could have caused it to mushroom.

The lost compression... That's just never good. Probably just stick rings, but you need to track down the root cause. I.e. find the air leak.

Thank you both!
I'll tackle both

Ive loosened the clutch cable and the kick start wasn't fixed. Kick start gear on the christmas tree perhaps?

Describe "wasn't fixed."

I think we already determined you've lost compression, right?

For the clutch, try putting the bike in gear and pushing it. Does it (try to) turn the flywheel crank? If so, then the clutch is probably okay-ish. If it doesn't, then you need to pull the clutch cover and see what the pressure plate and plunger look like to start.

Pictures of those will help a lot with diagnosing.

Thanks. I'll try as soon as I can.

When in gear, the scooter rolls but not in conjunction with the flywheel. Here are some pics of the head I removed today. I also see the exhaust mark on the frame near the top of the head that could indicate a leak causing lost compression.I was happy to see that the cylinder does move with the turning of the flywheel. The cylinder does not have a hole in it either.
So most likely a clutch problem and loose head cylinder studs?

You have a major seize, looking at the aluminum smeared on your cylinder. That'd explain the lack of compression.

It may be repairable, but let's get a look at the clutch next.

Heres the clutch cover:

With the cover off, the kickstarter moves in conjunction with the axle, flywheel, and piston. Also, if you look really closely there is a gouge in the crown of the piston.

So perhaps I will overhaul the clutch and then decide whether to have the cylinder and piston polished or replace it with a new head combo.









Last edited by baddug on Thu, 14 Sep 2023 21:08:35 +0000; edited 4 times

Piston crown says Jetting was at least a mile too lean.

Took the clutch off and found the retaining ring had dislodged. Also found some scoring on the "primary" drive gear.

Nothing to worry about with the primary gear, it looks like.

You need to figure out why the clutch circlip came loose--if the basket had spread or it just wasn't well installed.

If the basket has spread, get a 7 spring clutch and install that instead. Your plates look pretty thrashed, so you're probably going to be pretty close to replacement cost anyway by the time you get a new circlip and plates.

The seven spring can handle the loads of a mild tune, you just need to break of a little bit of the oil guide in the cases to install it. I did it on my SprintV motor years ago and haven't had any issues--and I thrash mine about as hard as anyone.

Any preferred brands of 7-spring clutch?

Buy a Cosa clutch. Everything better than a seven spring.
Doesn't look very oily in your clutch housing. Any oil in it?

Not much oil in there.

What Jack said.

I forget that normal people can't just reach into the parts pile and grab a spare clutch.