Bradley,
Try this first:
1. Remove the fuel line from the carby and check the flow of petrol.If it is very slow replace the fuel tap.
2. If fuel flow is ok then remove the screw in the centre of the carby and check that you don't have a blockage as it is the jet.
3. Also check the fuel cap as it should have a small hole in it. If it is blocked clean the hole out.
Regards,
Bruce