The fuel tank on the MGA is vented through the fuel filler cap, which has bothered me quite often. With more than half a tank of fuel and some spirited driving (serious autocrossing) the vented fuel filler cap can allow some fuel to spill down the back of the car body. Also over filling the fuel tank and parking it in the sun on a clear warm day can cause expanding fuel to overflow at the filler cap.

When this happens you should hope that the rubber grommet between the filler pipe and the car body is in good condition and held tightly in place, because if it isn't the fuel may well spill into the boot ("trunk space" for us yanks). Fuel spilling over can also stain or otherwise damage the paint finish. It also occasionally draws some concerned remarks from SCCA track officials, partly out of concern for the safety of the vehicle, and partly from concern that fuel spilled on the track may be a hazzard or adversely affect other drivers. In short, there is nothing good that can be said for spilled fuel.

I know what I want to do to this fix problem, but have yet to figure out how. Okay, maybe I just haven't properly applied myself yet. The fix would be to install a sealed fuel filler cap and a vent pipe. The sealed fuel cap would likely require soldering a new filler cap fitting onto the original filler pipe in place of the original top end fitting. The vent I have in mind would be a small tube connection in the side of the filler pipe just below the filler cap (inside the boot). Connect this to a metal pipe (for safety reasons) running along the corner of the wheel arch and the top of the boot to the highest point in the boot, right side top front corner. At that point attach an in line filter (as a dirt trap), and pass the metal line through a (newly drilled) hole in the inner fender, then bend downward slightly to terminate inside the rear fender, ahead of the tire. For protection against mud splash it might be good to terminate the vent pipe ahead of the forward splash panel. This would give a totally sealed fuel cap for no spill while still providing for ventilation of the fuel tank.