Hello Andy
Yep have tried swapping cdi aswell no difference! Have the lower exhaust off looking through the port, piston seems ok! But there are a few score marks on the transfer ports just above the port bridges! I'm starting to think I may have a damaged skirt on that piston! I'm not sure but this could be causing the blowback through the carb and making the carby look dry! I have also put my hand over the cold exhaust while running and it won't stall the engine,hand on the good cylinder exhaust I can stall the engine if I hold it there! To me this would suggest the transfer ports are leaking back to crankcaseThe engine from 3-4K up seems to heat that cylinder and visible smoke!but from idle to 3-4K it blows back and coughs! Does this sound like I might be heading the right way? I'm hesitant in pulling the barrel until I can get hold of some gaskets and rebuild kit!
Thanks
Tim