I have noticed that my juddering power loss only occurs on a low tank (amber light) after slowing or braking abrubtly. If I keep her topped up with more than 1/4 tank of Optimax, I dont get this power loss.
Just thought Id share with those who have had the same problem. I guess the fuel line from the tank comes from an area that can be sucked dry under braking on low fuel,and leave an empty section of fuel line for a few moments?