MotoGP God
Posts: 18,275
Join Date: Apr 2002
Location: Oxford
Mood: Its ONLY a Bike Club
check the tank breather, I have one bike that does tha same sort of thing, its not a duke. Opening the filler cap sorts it and as I open the cap you can hear the air rush in to fill the vacuum. The bike was OK all summer only does it in the cold weather.