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Vintage Vespa Forum

VNB Stalling

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Robmc Robert McConnell
Sydney, NSW, Australia   AUS
Hi All
New owner here and enjoying getting my hands dirty.

Here are my symptoms, is there a doctor in the house. Starts on 2nd or 3rd kick with full choke and a touch of throttle. If I let it run and it begins to warm up, when I slowly ease off the choke to about half, the revs actually start to climb. If I then close the choke lever it will stall.

It starts up straight away after it’s been for a run but still stalls, maybe not as bad. I have tried to adjust the idle screw but it does not make much difference, I can tighten it all the way up and it won’t stop the idle

I can ride it but it does stall if I don’t feather the throttle. I have changed the spark plug, photo below of the old plug. I have opened the fuel cap to see if there was a blocked breather hose but it makes no difference.

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OlympiaScooterCompany Silver Member Matthew Gatlin
Olympia, WA, USA   USA
Hello Robert,
There are several possible symptoms here and unfortunately several potential diagnosis here too:

1. If the scooter is not wanting to idle correctly it could be several factors. Try first using carb clean with the red straw and shoot it around the base of the airbox. If there is any fluctuations in the idle, then it could be an air leak caused from a worn gasket (case to airbox, or airbox to carb) or warped carb or warped airbox.

2. Seals... ugh when was the last time the seals were replaced?



Matthew Gatlin
Olympia Scooter Company
Cell: 503.954.4043
Email: sales@olympiascootercompany.com
Website: www.olympiascootercompany.com

Robmc Robert McConnell
Sydney, NSW, Australia   AUS
Hi Matt
Looks like to were right on the money. When I spray the carb cleaner around the base of the air box just before it sounded like it was going to stall, the revs would come back up.

I have enclosed a photo of the air box removed. It does not look like there is a body to air box seal. Also the air filter looks ropey but I am not sure if this is normal.

What do you suggest, carb rebuild or just airbox to body seal.

Thank for your help, I am just learning but still enjoying myself.

Thanks
Rob

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OlympiaScooterCompany Silver Member Matthew Gatlin
Olympia, WA, USA   USA
Hello Rob,
That is the air filter which sit's on top of the carb. (no gasket between the air filter and carb)
Take the carb off and undernethe the carb is the first gasket, remove it and there is a flat head screw, remove that to loosen the airbox. Once you loosen the airbox you can lift it up and see the second filter.



Matthew Gatlin
Olympia Scooter Company
Cell: 503.954.4043
Email: sales@olympiascootercompany.com
Website: www.olympiascootercompany.com


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OlympiaScooterCompany Silver Member Matthew Gatlin
Olympia, WA, USA   USA
sorry, second gasket



Matthew Gatlin
Olympia Scooter Company
Cell: 503.954.4043
Email: sales@olympiascootercompany.com
Website: www.olympiascootercompany.com

caki Joe Caran
Sydney, NSW, Australia   AUS
Hi Rob,
I'm from Sydney Hills district. Restoring my Vespa VBC and enjoying it.
Let me know if I can help.

Regards,
Joe

Robmc Robert McConnell
Sydney, NSW, Australia   AUS
Hi Joe
That’s fantastic news. I need all the help I can get. I work in Seven Hills in the week. I will drop you a private message with my details.

So, I thought I would start at the simplest area first fuel tank and tank tap. The fuel line is solid and as old as the hills, so that will get changed. I checked the flow from the tap and it was poor. I am not sure if the breather is semi clogged, I also see there is a small breather hole in the tank cap, is that just an expansion hole.

Anyway, carb rebuild kit to be ordered tomorrow along with a new fuel tank tap. If the problem persists after that. I will be back.

Cheers
Rob

Robmc Robert McConnell
Sydney, NSW, Australia   AUS
Hi
Just a quick note to everyone to say thanks for your help.

I replaced the tank tap because the fuel supply had air in it and seemed very slow and the brittle fuel line. I also rebuild the carb and found a few gaskets missing.

This has solved the problems and she starts up first time and runs well. The spark
Plug is a bit sootty and I have tried to tune the carb as this is running rich.

Joe was a big help by helping remove the tank tap and hopefully I can return the favour in the future.

Now onto the next area.
Cheers
Rob

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