My 78 280Z exhibits some bucking but only below a half a tank of gas. I has been explained to me that the fuel hose in the tank may have a hole in it and when the fuel gets low it starts sucking air & fuel. I fill the car up & it runs fine. The gas tank has been redone, fuel filter cleaned etc. The only way to fix is to pull the hose and basket by drilling another hole in the tank. The fuel tank seems to be a weak point on these cars especially when the car isn't driven much and allowed to sit. I have been told to keep the tank full when storing.