liam your right they are junk,check this take the air filter hose off the back off the carb and put your finger inside the venturi and make sure the slide lifts all the way up smoothly and comes down again slowish.as these do have a habit of the slide spring fouling up and jamming the slides travel whcih in turn stops air flow and also the main jet cannot operate with the slide needle stuck inside it.
adam bike doctor
May 2010