Fuel Consumption Issue......

Lets assume that it is leaking, but mostly when driving, and not when standing. Have you asked someone to look under the car while you rev the engine? It must be bubbling over or coming out somewhere. The only other thing I can think of is that your choke isn't adjusted properly, but that normally wouldn't give you that bad consumption. Tom

I remember having the same symptoms once, which was fuel coming out of an overflow on one of the SU float chambers, caused by dirt in the needle valves holding them open, and this would not show up when the car is parked and engine off, and fuel would evaporate immediately on the hot exhaust when driving.. not very safe!!

Been thinking about this some more & I vaguely recall that there is an electric thingy hidden right up under the rear seat pan inboard of the rear chassis rails. Would that be a secondary booster fuel pump?

Fuel pump diaphragm leaking. Does your oil smell of petrol? Though you seem to have lost a heck of a lot for it all to have drained into the sump and not been noticeable. Or a rust hole in the top of the tank so it sloshes out when you're driving but nothing happens when stationary.

shouldnt have this much effect, but i had a scarey incident at the start of this year, was checkign all my fuel lines, and noticed that the metal shaft that the fuel hose clamps to going into the fuel pump had come loose from the pump and was just sitting in place!

I think one of your carbs has a sticky plunger, maybe a rough spot on the inner face of the carb or the damper is making it hang up and your carb is drinking vast amounts of petrol because the needle's not sat at the right level......maybe, or perhaps your brakes are binding a bit, has there been a change in performance. If it's sounding a bit rough is it struggling to pick up as you drive away? Keep at it mate, you'll run out possibilities eventually. As Sherlock Holmes would say " When you've eliminated the impossible, whatever remains, however improbable must be the truth"