I have a Ford Fiesta 1.2 Finesse 04 plate, petrol engine. When the fuel level goes below 1/4 of a tank, the car starts stuttering, like it's losing power, then suddenly gets it back again. The lower the fuel goes, the worse it gets. It's quite unnerving when trying to overtake on the motorway when you suddenly momentarily lose power, especially with another vehicle behind you. When I have over 1/4 of a tank of fuel, it runs absolutely fine. The most feasible suggestion I've heard so far is that where the pick-up pipe or tube feeds into the tank, there may be a hole or a crack further up the pipe so that when the petrol falls below that area, the hole or crack is then exposed and is sucking in air. Any ideas please?