Modern Vespa

Not sure what's going on here. I just rebuilt a Vespa 100 and everything seems to be working well. Except for this odd phenomenon:

When I start in neutral first thing in the morning, and then shift into first, the bike sometimes behaves as if the clutch isn't working at all. There's a heavy clunk when I shift, and the engine just snaps into first gear, even tho I'm gripping the clutch handle back and first gear should not yet engage. This morning it happened twice and killed the engine.

After going through this process once or twice, the shifter begins to operate correctly, and it's fine for the rest of the day!

I'm a noob and just trying to figure it out by thinking it through. The bike is behaving, first thing in the morning, as tho the clutch is stuck—it never releases. So when I start in neutral and then try to activate the clutch to shift into first, maybe the clutch plates stay stuck together? That would be one explanation for what seeems to be happening—that I'm unintentionally just throwing the bike from neutral to first with no clutch, even tho I'm depressing the handle. So, big clunk and then the engine dies.

Is the likely issue just clutch adjustment? Maybe the plates somehow get a bit stuck overnight, and need to be pulled even further apart to work properly when I first start in the morning??

Or might there be something else in play?

Thanks.

Try backing out the adjuster next thing to try.

In my experience of one (stock clutch/cover), the window between stalling in 1st and clutch slipping is very narrow.

Do you know how much gear oil you have in there?

Ray8: Thanks very much. Yes, it turns out it was an adjustment problem. It was a new cable, and I think it was stretching. By the end of the day I had no clutch at all.

So I started playing with the adjuster and, yes, as you say, the window for getting it right was pretty narrow. Got lots of different shifting kinks until I finally got the adjustment right.

I'll ck my gear oil too. Thanks again.

Clutch adjustment or too thick or too much oil would be my guesses. It is not uncommon that you get a small jolt when shifting from neutral into gear even on any bike as the oil in the clutch will transfer some force, especially if cold, but it shouldn't stall out the engine

Glad you got it sorted out. My first reaction is always to adjust the clutch tighter when I had problems with it, but this made it worse. Loosened it a little and it worked great.

Surely you would have noticed that at the lever ? May also have slipped at the trunion.

The lever was still pulling. I think the cable had just stretched a bit, in the week since I installed it, and that little bit was enough to keep it from fully disengaging when I pulled the lever.

Or the pinch bolt might have slipped, tho it didn't look like it when I was checking things out.

As I say, I'm new and still trying figure out the various relationships and what's going on inside where I can't see. Experimenting, I tried the adjuster all the way out, and all the way in. All the way out, and the clutch was permanently open. All the way in, and the clutch wouldn't release. Finally found a position somewhere in between where things seemed to work as they are supposed to.

Amazing the differences that can occur in that 3/4" of adjustment.

Took it around the block after dinner. Seemed OK. But will give it more of a real test today.

Typically, there should be only a few mms of free travel before the cable pulls the clutch arm which pushes the plunger ( would be a throw out bearing in a car) in the cover to contact the pressure plate on the clutch.

When you set the trunion on the cable, first move the clutch arm forward against its spring to where it just makes contact with the pressure plate. You should feel it make contact before it pushes the springs to disengage the clutch. What you are aiming for is setting the plunger just off the pressure plate. That's where the free play at the handle bar lever is. Make sense ?

If you set the cable trunion with the clutch arm all the way back at rest and the adjuster all the way in, you'd be lucky if you could disengage the clutch without the adjuster all the way out and the lever almost to the handle bar.

I pull and tie the lever forward with a piece of wire so I can set the trunion properly. This is a bit fiddly. I usually set this tight with the adjuster about 1/2 way out so I can fine tune the free-play. Sometimes takes two shots...
Hope this helps.

Thanks. Very helpful. That makes a lot of sense. Will ride more today and see if it needs fine tuning. Cheers.

Moto64 has you sorted with that info. I'll just add that the manuals call for 2mm of free play at the lever before it engages the clutch.
Set your barrel adjuster somewhere in the middle when you attach the cable that'll give you enough adjustment to dial it in to 2mm.

Fantastic! An actual number to shoot for. Actually, offhand, I think that's about where I am now, but I'll go out and check in a bit (as soon as the fog lifts). Thanks.

Good clear description and I agree w/ everything you said except this. Cables will stretch but don't shrink, so I do the same but maybe only 1/4 of the way out coz it seems like I'm usually tightening the clutch cable as things wear and stretch.