Vespa starts moving without engaging throttle
Post Reply    Forum -> General Discussion
Author Message
Lurker
Joined: 21 Mar 2019
Posts: 2

Thu Mar 21, 2019 7:38 am quote
Hi all,

Newbie here. I've justed purchased a 2ndhand Vespa LX 50 4T. She's from 2013 and only has around 5000km. She has also got a complete check-up about a year ago but there's still one problem. When I start the engine the rear wheel starts spinning without opening the throttle. So when I start the Vespa I really need to hold down the brakes, otherwise it starts moving. Once I start driving there's no problem anymore, and actually the problem dissapears. When I take a stop somewhere (with the engine still on) the wheel doesn't spin anymore. The problem, thus, only occurs when I start it. The seller, one of my colleagues, told me that it has something to do with the valves but as I'm a complete newbie to scooters I don't have a clue.

I'm planning to bring it to a garage but I'd prefer to have some idea upfront about what the problem could be.

Thanks (and sorry for my English, I'm not a native speaker!)
Enthusiast
2009 GTV 250
Joined: 13 Apr 2015
Posts: 94
Location: Mountain View, CA
Thu Mar 21, 2019 8:12 am quote
I'm not familiar with the carbs on those bikes, but a possibility is that there is a higher idle when choked from a cold start, and the higher idle is engaging the clutch and spinning the wheel. When the bike warms up, the idle drops, and disengages the clutch at a stop.
Hooked
2007 GT200, 2008 Yamaha C3
Joined: 27 Jul 2012
Posts: 488
Location: Denver
Thu Mar 21, 2019 8:48 am quote
What you are describing sounds like the small clutch springs are worn out. This will cause the rear wheel to engage at very low rpm. You see no increase in idle speed upon start up? Seems odd on such a new scooter with low miles. I ran into it on a 50cc Yamaha with 18,000 miles. Idle was choppy and caused vibration at a stop. This went away when the rear brake was applied. Rear wheel spun when on the center stand. Clutch rebuild, and it stopped.
Hooked
2005 Stella 2T, 2014 Stella 125 Automatica
Joined: 20 Jul 2018
Posts: 100
Location: Staten Island, NY
Thu Mar 21, 2019 9:10 am quote
jjhenry5 wrote:
I'm not familiar with the carbs on those bikes, but a possibility is that there is a higher idle when choked from a cold start, and the higher idle is engaging the clutch and spinning the wheel. When the bike warms up, the idle drops, and disengages the clutch at a stop.
This has been my experience on my 14 Stella automatic. I agree, sounds normal or maybe idle jet slightly rich/idle set a little high. I've explained my similar issue here

http://modernvespa.com/forum/post2309201#2309201

Once i sorted out my air mix screw i was able to get the out of control idle at cold start under control, but fyi, the wheel will always rotate when first starting cold due to choke. Key is to get the throttle adjustment screw (idle) set so the idle is just before the wheel starts rotating when warmed up. If you have it set too high when warm, then when cold starting it will go crazy until choke turns off.
Ossessionato
BV350, Primavera 150, Yamaha Zuma 125
Joined: 06 Jun 2013
Posts: 2434
Location: The Twin Cities of Minneapolis/Saint Paul, Minnesota
Thu Mar 21, 2019 9:31 am quote
Nothing to worry about if you can stop the wheel with a light application of the brake.

It has nothing to do with the valves.
Hooked
2005 Stella 2T, 2014 Stella 125 Automatica
Joined: 20 Jul 2018
Posts: 100
Location: Staten Island, NY
Thu Mar 21, 2019 9:38 am quote
JKJ-FZ6 wrote:
Nothing to worry about if you can stop the wheel with a light application of the brake.

It has nothing to do with the valves.
Agree with jkj. If you can't bring it under control with a free solution of idle adjustments and light brake application, then you should try the non free solution abner gave.

Shiftys have manual clutch that you engage/disengage. Automatics must do it internally through throttle application overcoming internal forces of the clutch springs. So either you are getting too much rpm or springs aren't strong enough for base idle rpms.
Hooked
GTS 300ie Touring
Joined: 03 Jun 2018
Posts: 226
Location: Limassol, Cyprus
Thu Mar 21, 2019 11:24 am quote
JKJ-FZ6 wrote:
Nothing to worry about if you can stop the wheel with a light application of the brake.

It has nothing to do with the valves.
+1

This is quite normal. Mine does exactly the same. It's the result of the automatic choke increasing the idle speed when the engine is cold. So long as the wheel spins only slightly after the engine has warmed-up, you have nothing to worry about.
Addicted
lx 50
Joined: 09 Oct 2017
Posts: 740
Location: Brighton
Thu Mar 21, 2019 12:13 pm quote
Loads of good correct comments above.

Guessing your not a mechanic and a total newb.

When the engine is cold the choke puts extra fuel in, which slightly increases RPM of the engine.

This slight increase is just enough to make the centrifugal clutch engage at the rear wheel and cause it to start spinning.

Then once your engine is up to temperature the choke no longer puts in extra fuel so your RPM drops to normal tick over at idle.

So it could simply be your idle is set to high, this is best set once warmed up, set as low as possible without stalling. That would be my first check.

I doubt itís the choke as itís clearly working and canít over work.

After that it could be the 3 clutch springs, but at such low mileage doubt it......but could be.

Bottom line, the back wheel should not spin at idle cold or hot.
Hooked
GTS 250ie Super, Italjet Velocifero, Scarabeo 150, S50,ET2
Joined: 22 Nov 2016
Posts: 307
Location: Winston-Salem, NC
Thu Mar 21, 2019 5:23 pm quote
My S50 idles very high like 3500rpm when the enricher is on. of course I get some wheel spin. Once the enricher kicks off it drops to 1800-1900 rpm and is good to go. Get a tach and adjust your idle when the engine is warm and it might slow the wheel down some.
Hooked
2005 Stella 2T, 2014 Stella 125 Automatica
Joined: 20 Jul 2018
Posts: 100
Location: Staten Island, NY
Thu Mar 21, 2019 5:27 pm quote
Pinkscooter wrote:
My S50 idles very high like 3500rpm when the enricher is on. of course I get some wheel spin. Once the enricher kicks off it drops to 1800-1900 rpm and is good to go. Get a tach and adjust your idle when the engine is warm and it might slow the wheel down some.
I've set the idle on my 2014 Stella to 1200 rpm and the wheel just barely starts to spin on stand with choke and is static without choke.
Lurker
Joined: 21 Mar 2019
Posts: 2

Fri Mar 22, 2019 2:32 am quote
Wow, thanks for all the useful replies!

I decided to give a quick call to the Vespa dealer to ask how long I would have to miss my scooter for repair. But when I explained the issue they told me that this is very normal for the LX 50 after a given period, and there's basically nothing to repair. They get high in RPM when you start the engine but this usually stops after a few minutes when stationed. Usually I just start the engine and drive off but I will try to wait for a couple of minutes and see what happens.

And, indeed, as mentioned above this has nothing to do with the valves according to the dealer. If there would be something wrong with the valves I would have trouble starting the Vespa and it would make a ticking sound but this is not the case.

Thanks for the help!
Addicted
lx 50
Joined: 09 Oct 2017
Posts: 740
Location: Brighton
Fri Mar 22, 2019 4:59 am quote
Kinda disagree with their verdict tbh.

Yeh maybe the wheel might spin a small amount, but you mentioned it wants to ride off with you on it unless you apply the brake.

Thatís too fast. Yeh you can live with it, but for maybe just a few adjustments it might be solved.

Go on YouTube and search your scooter and adjustment of idle. Your not going to brake anything and it might work!
Enthusiast
Looking
Joined: 18 Feb 2019
Posts: 53
Location: Tampa
Fri Mar 22, 2019 5:47 am quote
Just curious.
If the Vespa is on the side stand when this happens, and unattended, is it enough to push the bike forward and fall?
Ossessionato
BV350, Primavera 150, Yamaha Zuma 125
Joined: 06 Jun 2013
Posts: 2434
Location: The Twin Cities of Minneapolis/Saint Paul, Minnesota
Fri Mar 22, 2019 6:26 am quote
Allens wrote:
Just curious.
If the Vespa is on the side stand when this happens, and unattended, is it enough to push the bike forward and fall?
That's why you don't put a scooter on a side stand with the engine running.
Team Scooter Trash for Petfinder Foundation   Vespa Wasp Pin Badges   AF1 Racing Vespa Austin
Post Reply    Forum -> General Discussion
[ Time: 0.3714s ][ Queries: 24 (0.0620s) ][ Debug on ]