Hi grumpy. I finally got around to removing the carburetor and gave it a good clean. The intake screens are also clean and as I said previously I have already replaced the diaphragm. I did however notice the base plate of the carburetor where it mounts to the fuel tank was quite warped so I fitted two gaskets on reassembly in the attempt to reduce any suction of air. There doesn't seem to be any fuel seepage in the area so hopefully this isn't causing any problems. So after this little exercise I'm still no further in front, the engine still takes around 15 pulls to fire from cold start frown. I feel I'm running out of options I may just have to find a replacement carburetor.