Modern Vespa

Hi all, i have a confounding problem, for all who love a good vespa challenge!!!

I have a PX200, bought new in 2004. Ridden daily for a few years, then sat in the garage for about 5 years till I recently took it out to commute again.

But the commute, while initially running well, soon became a case of start up, rev, take off as soon as possible, till while slowing down for a set of lights, the engine would stall!

We (my father and i) had suspected a fuel blockage, as the startup electricals appeared OK, and we were seeing a spark at the plug. Just in case, we replaced the plug with a new one and set the gap at 0.6mm as recommended in the Haynes VESPA Service and Repair Manual for 1978-2006 Models.

We took out the combined fuel/oil tanks with the hoses attached and replaced the now-discoloured and hardened plastic fuel pipe with a new fibre-reinforced rubber one, experiencing some difficulty in pushing it through the hole in the wall/body separating the cavity for the tank from the carburettor. Due to the difficulty of accessing the piping under the tank while re-installing, the fuel hose might be a little longer under the tank.

We then took off the air filter casing, removed the air filter, washed it in petrol and left it to dry, and noted that there seemed to be an excess of oil in the base of the area which we traced to a loose oil pipe at its connection into the oil metering device which joins to the carburettor. We tightened the nut and washed off the surplus oil.

We then removed and completely dismantled the carburettor. We checked the float was sound and not leaking, as well as removing and cleaning out all the jets before reassembling it all. We tested all were clear and unobstructed by blowing air through all jets and connecting holes in the body of the carburettor.

Finally, all was reassembled to our satisfaction, refilled the fuel and oil tanks and started the engine. It all seemed to run well. After allowing warm up for 1 min or so, we adjusted the idle screw after optimising the mixture screw and again, it seemed to run well. Hooray!!

That evening it drove without any hiccups about 5km.

BUT, it was only the next day when driving to work, that it began to stall and with increasing frequency as i progressed painfully to work. Needless to say, I left it at the scooter workshop that evening.

They called within a few days to say they had just cleaned out the carburettor (which I had already done!), and it was running fine, and it wasn't stalling any more. Within 2 or 3km, of happily riding it home.... lo and behold... it stalled while sitting at the traffic lights. I limped it back to the shop, now with a new issue - whatever they had done at the shop, not only did it stall at slow speeds, but now at higher speeds (2nd or 3rd gear) it would just die!! And would not be able to start except after a few long minutes of sitting patiently at the side of the road.

For my dad, who was a scooterer back in the '60s and '70s during which he did his own servicing on these mix-your-own-fuel 2-strokes, it really appears like a fuel-starvation issue, unless there is an electrical ignition failure that arises as the engine heats up. Obviously, the fact that the workshop virtually repeated all the remedial measures that we had already tried with no improvement, suggests that either both we and the workshop overlooked the same fault or that the fault lies elsewhere.

It may be possible that as we had taken out the tank and refitted a new fuel pipe and, in the process of re-installing the tank, the new fuel line may have been, unknowingly, doubled over in the space between the underside of the tank and the floor of the scooter's cavity. If so, this could have pinched or partly closed the fuel line resulting in it only allowing the fuel that was trapped in the line between the 'pinch' and the carburettor to feed the carburettor when one takes off. When this fuel was used up, the engine would be starved of further fuel and die. Then, after waiting a few minutes or more, a little more fuel would trickle past the 'pinch' to feed the carburettor, so then, on attempting a restart of the engine, this would fire up and run for a short period until again used up.... and so on and so on.
This seems to fit the exhibited symptoms, doesn't it? As the exhaust does not exhibit excessive smoking, we find it hard to accept the notion that the engine stops because of excess petrol leaking past the float chamber, which is what the workshop suggested, as a possible cause.

Any help with observations and suggestions would be much appreciated!!!!

Did you check if the fuel tap is clogged ? Also check for cracks on the ignition coil casing and HT lead . Hope this helps .

There could be several things going on here:

If the fuel line is 2 feet long and ran properly from the tank to carb there should be now kinks. Check there.

After sitting a while in storage the CDI's on these scoots go bad. It's just age and/or sitting in a hot place like a shed that causes the issues. Scooter runs find until the motor gets hot and the CDI stops working properly. The spark plug cable can get brittle over the years, too. Try replacing the CDI and spark plug cable and see if the stalling stops.

Seals can go bad over the years from sitting but since you're not seeing a lot of extra smoke from the exhaust, that maybe not the issue. When changing gear oil check for the smell of gas in the drip pan of gear oil.

Good luck!

What is a CDI?

Welcome to M.V.
https://www.revzilla.com/common-tread/what-is-cdi-what-does-a-cdi-box-do

Spark plug wire connects to it because it provides the spark for the motor. Electronic ignitions uses a CDI's. An ignition coil is used for points ignition.
https://www.sip-scootershop.com/en/product/electronic-unit-piaggio_85000000?cr=e993ab67-6807-4109-bbed-f6374ebf9f9b&gclid=CjwKCAiA4KaRBhBdEiwAZi1zztBUpJm4f03XV96M9LuYHe8TAs0fWi-yapzjsGlsB0XnZ-lQ4-NM2xoCpAAQAvD_BwE

Hi guys, thanks for all your input!

So, for sure we hope to check out ignition coil, and HT lead, as well as going over the fuel line, before even attempting to open the CDI which the useful link @sledge posted, says is like opening a sarcophagus!!!

@roydwc - thanks for your thoughtful input

Will keep you posted!