Just a quick update, I decided to remove carbs to give them a clean and there was a load of gunk in the bowls so cleaned out with carb cleaner and blow them out with the compressor, so had a look at air filter while I was there an found that somone has made a filter From one of them foam filter sheets you cut yourself but has been made very badly, doesn't even fit the airbox there is half inch gap most of the way round, so I've just ordered a new one see if that helps