Newbie: vespa cutting out - not much power

what could be causing a 125cc small frame scooter from cutting out all the time, specially when going slow when turning around corners etc. Also dosn’t seem to be much power coming through not going as fast s it should.

what can be causing it to cut out

It sounds funny,
But have you checked the wiring loom is not being pulled taught, and maybe earthing out as you turn the handlebars,
It has been known to happen,