The problems continue. By advancing the ignition the overheating has ceased. However,although it starts very easily,it is now only running (albeit very well) on one cylinder. I have changed the transfer port gaskets, changed the crankcase door gasket. Swapped the plugs over.Swapped the plug leads over. Attached another plug to the plug lead (scintillating spark), what else can I do or check ??? So near and yet so far !!!