the mixture is too rich i.e too much fuel to air percentage,you need to firstly check the throttle slide to see if you can make it a bit leaner and see if it will run like that,take the throttle slide out by undoing the small screw that holds it in on top of the carb,then take the cable out of the slide and look at the postion of the e clip on the needle .if its not already there move it to the slot furthest from the pointed end of the needle try and run it and see how it is.if this doent work then you need to move the eclip back to the middle slot and then get a smaller main jet go down about 5 or ten on you rmain jet ,so if it has an 80 main jet try a 75 or 70.i start with a standard jet and then drill it slightly bigger until its right using jet drilll they are very small and go right down to 0.2mm so two tenths of a millimetre!you can always play with the eclip postion once you have rejetted it moving it the clip towards the pointed end to make it richer or away to make it leaner.
adam bike doctor, January 2010
