Modern Vespa

Hello, Can anyone help me? I have this problem, I have a Spanish VNA 125 vespa, the vespa starts ok when it´s cold. I run with it and when I stop it, If I start it inmediatly it starts without problems, but If I start it after few minutes It doesn´t start. I´ve already changed carb, fix the points, check ignition and all is ok. Asumming up, My vespa doesn´t start when is cooling and it stars when is cool.Thanks I´m sorry aboy my English

Welcome.

Maybe this thread can help you:

http://www.modernvespa.com/forum/topic37080

thanks I saw it, but all electrical parts are replaced, also carb, so I don´t know what it happens

hows your plug ??? you should change it sounds like a common fouling but you might have some other issues going on too ?

Thanks, It was the first thing I do. But nothing. When my vespa is cool no problem. The problem to start is when then vespa is cooling. Strange but real!!

All electrical parts are replaced? That doesn't necessarily mean that the HT and / or condensor that are on your bike are currently good.

Are you closing the fuel tap after a ride and letting the fuel burn out before hitting the kill switch? Sounds like it's flooding.

I was wondering that myself. Good call.

Sounds like a problem I had many years ago. Once the scooter is stopped, heat works up from the cylinder to the carb, resulting in fuel vaporization in the carb.

Does youir engine run very hot? Perhaps retarding the timing a bit, or a slightly larger main jet would help.

Mike

thanks to everyone, I will try to change main jets. Because the timing was checked at it was 28º

Is this standard procedure, to consume all the fuel in the line before shutting off the engine? I normally hit the kill switch and then turn off the petcock lever (to prevent fuel spilling if the scoot was knocked over or whatever). Should I be running it dry, instead? Is there any danger of too much friction in the engine since as it starves of fuel it also loses the oil? Is it bad to let the carb and fuel line stay with some gas in it overnight?

Thanks for any replies and cheers,
phaetn

Punt. Just wondering if this is a good thing to do. Should I be leaning out the engine to stop it by turning off the fuel petcock rather that using the kill switch? Is it not recommended to leave fuel in the carb and fuel line overnight?

Cheers,
phaetn

In addition to the fuel tap, what stops all that gas from flooding down into your carb is a wee thing called a float needle. Its a wee brass thing that looks like a stubby tapestry needle, with a bit of conical shaped rubber on the end. That bit of rubber is your last defense against getting flooded.

Pic of float needle http://www.scootersoriginali.com/osc/product_info.php?products_id=752

You turn your fuel tap to the off position to prevent all the gas in your tank from putting tons of prssure on that bit of rubber. The pressure with the fuel tap in the on position will, over time, cause a ring to wear on the rubber bit of the float needle. This ring will prevent a perfect seal in the fuel system allowing drips of fuel to fall through the carb into the cylinder, and if the bike is left for a while, fill the exhaust with gas.

Its especially important to remember to turn your fuel tap off in these ethanol days, when rubber bit that contact gas wear out more regularly.

The reason shops tell people to turn their fuel taps off before the engine is cut is to get people into the habit of turning their fuel tap off. It does burn off a little fuel, relieving a little weight pressure from the stuff in the line, but not a massive amount. Honest to god, if we didn't tell people to do that hardly anyone would ever turn off their fuel tap. We get tons of fuel leak calls where its just that the fuel tap hasn't been turned off.

There is no need to run the carb and fuel line dry.

Andrea

Hi Andrea, would you also recommend consistently closing the fuel tap on a 2005 PX? - I only close it sometimes. I'm still riding here - my PX is filthy with the sloppy streets we have. Just got back from grabbing a coffee and a new plug and thought about your comments so closed the tap when I got back.

Yes I would. You'll prevent wear on your float needle.

As a note of interest we got another call this morning from a guy getting annoyed at me because he had an "oil leak". Turns out its petroil mix dripping from his exhaust and the guy admitted to only turning his fuel tap to the off position part of the time

The idea of turning your fuel tap off is that its preventative maintenance that will help avoid future problems. its an extra defense in the fuel feed system.

Andrea

Thx - will make it a habit. Funny, as I do it 99% of the time on my Sport but for some reason not on the PX

Thanks so much for the comprehensive reply, Andrea. Happily I turn the fuel tap to "off" as part of my dismounting routine. It's great to know the reason why it's so important and also that I haven't been doing anything wrong by not burning off the fuel in the line. Thanks again,
phaetn