Modern Vespa

I know David may be angry with me because some of you will think this is an advertisment. It may well be for those that live in the area and if I don't say it here then where else?
Thousand Oaks in CA. have some very fantastic service personel.
Thank you Jamison and Spencer.
A friend and I rode our two Vespa 250ie's to nearly 9,000 ft. elevation recently. After riding we put them on the trailer and trailered them to sea level where for some reason upon starting them we could'nt keep them running properly. They were both stalling. Since the 2000 mile service was very near, we made an appt. at Vespa of Thousand Oaks, CA.
I am sooooo happy with their fine service (they also did the 620 service on both scoots) They did the 2k service and the scoots are running like champs!!!
Don't know if it was because we didn't RIDE the scoots down from the high elevation or what, they ran fine at 9,000 ft. and being fuel injected there were no carburetor issues, but very strange that both bikes had the same symptoms. Anyone else have any experience of this kind after being at high elevation?
Vespa T O have truly earned my trust. Highly recommended!!!

Did you ever find out what was wrong?

I'm contemplating the purchase of a fuel injected scooter and often experience the change of altitude by trailer.

Did you fill-up at 9k'? If so, that's likely your problem. Density (aka pressure) decreases at a rate of 2.9% - 3.0% for each 1000 ft. of elevation above Sea Level.... Atmospheric Pressure @ 9000 feet = 10.5 psi vs 14.7psi @ Sea Level... The Fuel system on the fuel injected GTS is essentially sealed to prevent atmospheric venting (think Green). If you didn't equalize the pressure once at lower elevation by simply opening, then closing the Fuel Filler Cap, you effectively had a pressure differential which caused a slight vacuum in the Fuel system preventing fuel from flowing.

If you didn't fill-up at altitude, then I suspect that the issue lay with the Injector mapping (pre-programmed injector control). The ECU on the GTS is not as dynamic as those used in cars today. That is, it does not adapt so readily to changed variables, such as an 'instant' pressure differential, which is what you essentially had. Instead of using a Mass Air Flow Sensor (MAF) like cars now do, it senses the A/F mix by the lamda signal it receives from the lamda sensor on the exhaust (basically an O2 sensor) and then selects the proper fuel Map - takes longer, but still gets you there. The ECU adjusts the A/F mix by varying the pulse width (duration) of the injector - longer pulse injects more fuel, shorter pulse injects less fuel. At altitude, the pulse would be shortened to adapt to 'less' air. If shut-off at altitude, the ECU would have been using this 'leaner' fuel Map. Re-starting at lower elevation, still using this 'lean' Map, insufficient fuel would be delivered for the time necessary for the ECU to re-adapt and select a 'richer' (longer pulse) fuel Map, resulting in poor starting, stalling, etc. It would clear up by simply cranking the starter for a loner than normal period.

Probably too much information, but the question was asked.

I had the same problem coming down from Wrightwood to Rosemead.
I reset the computer myself by disconnecting the battery for 30 minutes, after that it ran close to normal but a little rough.

I sent it in to VTO so they could double check it and they couldnt figure out why it did that. If it happens again, disconnect the battery and reset the computer yourself. Then you wont lose time taking it into the shop.

Spencer is a good mechanic.

Manny