Update 2 - Swapped the carbs, swapped the coils, swapped the plugs and still when she runs poorly on the bottom - she starts well, when idling i cannot touch the top exhausts - the bottom is still only hand warm. She splatters petrol and oil out and whereas the top cylinder smokes blue the bottom is white and thick. I rechecked the spark and it looks fine to me. A bit clueless to what do now - any inspiration welcome !