A BIT OF INFO THAT MAY HELP SOMEONE WITH THE SAME PROBLEM.
my 40's ford is on a 6v system it has always been one of those that struggled
to start to the point of running the battery down. (stick with it)
the car had a new poly tank fitted but no sender.the wire was there hanging
i got a sender and put it in when i connected the sender wire there was no reading at the fuel gauge,
i connected a second wire and ran it the length of the car touched it on the back of the gauge with the ignition on (still no reading).
if i ran it to ground the gauge would go beyond full.with ignition on (not good).
after much swearing and head scratching, i spotted a resistor on the bulk head under the dash with 2 wires, i put the wire to 1 one of the connections
and the guage slowly crept up an registered correctly,blinding i thought.
so i ran a new wire(keeping the old one connected to the sender)as it would only get a reading withe the 2 connected.
then things got even better as i went to start the car it turned and fired right away the sluggishness had gone.
i know it is all part of the ignition system but don't really know why it helped the starting but it does.
i know this is long winded but it just might work for someone else perhaps if they have no reading at the fuel guage and slow starting.