Modern Vespa

Hey Folks,
Newbie here. I have a '61 VBB 150 Allstate.
I don't get a chance to ride it much, but when I do, it typically starts pretty well, but when it warms up it doesn't want to rev. I get stuck at traffic lights and have to walk it to the curb.
Throttle all the way, but it's almost like the cables not connected, but it clearly is mechanically working. If I work at it, for along while, sometime I could work it into a rev, and it'll keep revving as long as I don't let it go down to an idle. It idles fine.
I've cleaned the jets with and tried mixture and idle adjustments, but no change. Any suggestion, welcomed.

Skute61

Oil seal, clutch side.

Some things to try:
Remove the airbox cover and check that the choke lever is fully closing when you close it.

When this happens again, pull over and open and close the fuel cap (introduce air to the tank) to see if it changes things.

Drain the gear oil to see if it smells like gas.

Replace the spark plug.
The ignition coil can also go weird on you when hot, even though it worked fine cold. My symptoms were a bit different, but if there's no gas in the gear oil you might want to try another to rule that out.
Good luck!