I have a 1.25 fiesta and for some reason when it gets down to around a quarter of a tank it starts to bog. I have ran redex through the system to see if that would help but it still happens? Once I fill my car up it will run perfect until it gets to a quarter, could anyone help as to why this may be and what I can do to sort this? Thanks

probably collecting gunk from the fuel tank and choking the filter. I would suggest flushing the fuel system properly, as even changing the filter, it will continue to happen until the gunk has all made its way through to however many filters you change.

best answer is to drain the tank, disconnect the fuel lines, and work backwards, flush the tank thoroughly, get rid of as much of the cack as possible.

Then using a vacuum set, put some fuel in the tank and reconnect the lines, and vacuum the fuel through the pipes to try reduce the air bubbles

Then fill the fuel filter and connect it up and prime the filter properly.

Then disconnect the fuel rail and draw the fuel from the fuel filter to the fuel rail, in order to minimise the amount of air in the system. Then just start starting the car a few times.