Scooterotica

I finished my winter project around two weeks ago, covered about 4 miles running in, electrics giving me problems. Managed to get the lights and brake light to work after many hours fanning about. Decided to take it for a test run, hoping I could use it for work tomorrow, running in the new piston and crank.
LML125 Engine with
RD250 Reed Valve and Manifold Block.
28mm PHBH Carburettor
60mm Crank, 1.5mm Spacer and tested for Squish, all seems ok.
Polini 180 Barrel & Piston
Cosa Clutch
Gianelli Exhaust
PInasco Flytech Stator
Now got to the end of my road and it started to whine/rev like mad, tried to stall it as I have no kill switch, was not happening. Managed to get it into neutral and started free wheeling back down the street. Then it jump started itself and went like fk, managed to steer it into the drive heading for my neighbours van, pulling wheelies, could not stop the thing until I came of it. No damage done and no one witnessed the occasion, thankfully as most of them are bikers. Seriously whats all that about.

Throttle sticking or serious airleak, carb ,reed ,manifold area , or main seal failed or didnt go in properly..to test for the seal take the clutch breather off and start it, when it starts revving up put your finger on the hole and see if the revs drop.
Obviously it didn't ought to be jumping into gear and driving off , so you'll need to prevent that first

I had similar revving experiences and as cit205 say, its sounds like an air leak. In my case it was all related to the carb side. One instance the carb rubber split and the next, the carb sliding off the manifold on account of that stupid car radio hose that is sold. So i would look at your carb side first.

Must admit, your graphic description in the last paragraph had me laughing. We've all been there with our scooters deciding to do something that both attracts attention and immediately ramps up our stress level to real fear; whilst at the same time trying to look outwardly cool as if this is all normal.

As my carb slipped off, I was riding through a busy Skipton Sunday afternoon, awash with elderly day trippers. When suddenly 7000 screaming revs came on tap, causing me to slip the clutch, but still doing a turn of speed, I gripped the handle bars and smiled as I weaved chaotically through the afternoon jay walkers.

At least you didn't pull a wheelie and fall off.
I think I will strip the engine and rebuild from scratch. A good days work. At least I've got my brothers dining room to roll about in.
Cheers