Hi, in the carb there`s a brass jet (about an inch or so long) you can see the top of it sticking up if you remove the (figure of 8) carb gasket. Gently remove the jet by pulling it up, there is a small hole right down through it which is best cleaned through with the hair of a wire brush. Rebuild & refit, set your mixture screw to about 3/4 of a turn out from stop & give it a go.
John
March 2011