need advice - vintage Vespa running rough

any bike older than 25 years id recomend a full carb disasembly and cleaning beginning each year.

*grumble*

Can I just use some of that seafoam stuff instead?

Kara Things that I would do on a vintage bike at the beggining of every season, if I had one:

I would be inclined to drain the gas and replace it with new, just to be safe. drain it into a jar and let it sit- see if any water float to the surface or rust bits settle to the bottom.
You may have a clogged filter, (worth checking anyway) I would be inclined to check that Clutch cable for wear- when was the last time it was replaced?
replace the spark plug- or at least check the head for discolouration.
wd40 all of the electrical contacts

It is possible that the carb is causing your present issues or it could be a few items acting up.
It may not be that's it not getting any gas, it could be the air intake- check both filters to see if they are dirty.

Most engines will act differently in extreme weather conditions and need to be tuned occasionally.
( i drove an exotic car from california that was shipped here for a movie set, and the darn thing backfired because it was tuned to their climate and had to be reset to ours by a mechanic- scared the bejesus out of me- I thought that I hit something in the road and wreaked it)

I would also PM someone like Vince and see what he thinks, since he rides a '78 P2 and may have experienced what you are now.

Gasoline that gets old turns to a varnish like goo.First screw your carb's needle valve all of the way in. (Gently!) counting the turns. Then unscrew & remove it. Pull your float bowl & remove the pin that secures your float assy & remove it . Now you can get the goo out of your carb. Using the little plastic wand that comes with spray carb cleaner spray every passage you see including where your needle valve was. When you reinstall the needle valve screw it all the way in (gently again- if you damage it by forcing it you're in trouble! They're hard to find)and back it out the number of turns you did in the beginning. Usually this will fix the problems you've described. Your engine surging was causing the hard shifing. If this doesn't help your carb'll have to be removed & disassembled & cleaned. Gabe

Kara: Glad to hear your scoot is back in form. Ditto on the gasoline turning to goo thing. Gasoline begins to degrade and disassociate after 60 days. So.....if you are not going to ride your scoot for a number of months, or, you are overwintering it then Stabil works very well. Cheers!