Modern Vespa

My stalling problem at idle came back and the engine will only run if I keep revving it, then it suddenly fixes itself. So I'm cleaning and rebuilding the carb. I've ordered a new throttle rod for the slide, which was bent and had a gouge in it. But I also discovered the old throttle rod seal was too thin to fill the slot for it in the casting so air can get around it, and the one in the rebuild kit is also thin. Should I shim this in some way to get a better seal?

Also, the seal in the back of the carb box that covers the mixture screw is missing on this bike (and has always been missing). I ordered a replacement. Vespa seems to have gone to a lot of effort to seal this carb and carb box, but then they have a big air intake in the front of the box. It doesn't make much sense. Does anyone know what these seals are for, and could this have something to do with my stalling problem?

Mike Taglieri

The plug in the back is a summer plug. Remove during winter. Your stalking is something else. Clean up carb and rebuild. If you get same results then start looking towards ignition
System

I believe the "summer plug" is on top of the air box cover. The plug in the back of the air box is for accessing the mixture screw.

Both holes do allow some "extra" air in if the plug is missing, but not enough to keep the carb from being tuned. The one behind the air box is particularly easy to misplace and a pain to put back on. My guess is more than half of the old scoots here don't have it.

You do have the air hose between the carb box and body, right?

Those little plugs are to encourage all the air to come from the relatively cleaner, cooler space inside the body instead of from the relatively hotter, dirtier area around the carb box. I'm with socal, they aren't critical.

Thanks for the replies. With filtered gas in the fuel system and a totally clean carb, I'm hoping this will be the end of these problems.

But if Vespa cared so much about clean air, why did they use such a crappy air filter? I can literally see light through the mesh, but it doesn't look damaged in any way, so that must be what they thought was good enough. The other vehicles of that era tended to use paper filters or oiled foam filters (or, on the VW bug, an oil bath air filter). On my Norton, I've always used a K&N filter, but something like that would be way too big for this tiny space.

Mike Taglieri

The corse filter is a byproduct of the airs path into the engine. So, as the air travels from under the seat into the frame, by the fuel line, over that greasy mysterious plastic tray, through the bellow and into the air box most of the dust gets lost or annoyed.