1977 f-150 carb problem....

:banghead: we have a 1977 ford f-150 truck with a 6 cylinder 300 cubic inch engine. the carb that is on it was sold to us as the correct one, but isn't. we bought this carb at least 22 years ago. all the parts places we called list several different carbs as available. according to everyone we have called we have to get the number off the carb to get the right one, but the carb we have isn't the right one, so this is useless. how does one go about finding out which carb is the right one for this model? we have adjusted it and it just drinks gas. i don't mean mileage is bad, i mean we can see the needle go down as you drive, like 1/4 of a tank in less than a mile. at this rate we can't hardly drive to a repair shop. any help would be greatly appreciated.

Make sure the plugs are ok then take the card to someone thet can rebuild it, it sounds to me like the carberator float isn't working maybe stuck. good luck