Modern Vespa

Having power loss, missing, seems like more often when headed uphill, but not predictable. Not convinced it's a fuel problem although it feels like that (bike has a history of fuel - side problems as do many Vespie) - because it does not stall out as it usually has when was having fuel delivery problem. Instead problem persists for a while and disappears then comes back 5 minutes later.

Recently replaced (again) the vacuum petcock and have a 12v fuel pump inline after filter before carburetor, been there a while. Vacuum line seems good.

Was a problem with spark a while ago - bad / loose connection at coil, on 12v side I think - replaced plug, coil, wire, all seem good but not sure how to verify it's not spark problem

Will figure out eventually but ideas would be welcome!!

Many thanks!

Uphill power loss to me suggests that the variator, rollers, or clutch pulley are sticking so the transmission gets hung up in "high" gear. This can feel frustratingly like a fuel problem, but is actually the engine lugging.

So give the CVT a good once-over and see if that solves the issue. If it's a carbed LX and you don't know for sure when the transmission was last serviced - it needs it.

Thanks Juan, that's a good idea