Welcome to Miniriders.
I'm guessing it's got a blocked Pilot jet, the smaller one of the 2 that sits towards the intake manifold
You'll need to pull the carby off, and remove the fuel bowl fro mthe bottom of it
quickly dry the rubber seal to stop it moving out of shape.
find the pilot jet and take it out, you should be able to see through the middle of it, poke a thin piece of copper wire through it, 1 strand of electrical wire.
then there might be holes across the jet too, make sure they are clean and see though.
now under the carby where the Pilot jet came from, you should be able to see light through into the main bore of the carby, if not poke something through there too
blow the carby out well with compressed air.
blow it into the 2 or 3 small port on the air filter end of the carby, check that you can feel it coming out the bottom of the carby through the jet holes
Cheers, Craig