I've been lurking here for about a month . . .
I found a couple of threads on the subject of the fuel gauge system to be helpful, especially one of which that links to the MGA guru site:
Fuel Gauge Function
I've had my BJ8 for 21 years and in all that time, I've lived with an inaccurate fuel gauge and one that has to be tapped after starting the car to get it to move off the left pin.
Calibration seems fairly simple and is explained here:
Fuel Gauge Calibration
I used a 12 VDC source and a 100 Ohm variable resistor (potentiometer) in conjunction with a digital multimeter with an accurate resistance reading capability.
Using the information provided in the link, setting the resistance between the "T" terminal and ground (earth) was as follows:
70 Ohms = full tank
52.5 Ohms = 3/4 tank
35 Ohms = 1/2 tank
17.5 Ohms = 1/4 tank
Shorting the "T" terminal to ground (0 Ohms) = E
The above presupposes the sender is functioning as intended which is true in my case . . . as I had previously replaced it!
For those of you who have a gauge that sticks, here is a very easy fix that will not be visible to anyone except those who look at the gauge under a magnifying glass.
Under a magnifier, I had noticed a very small v-notch in the gauge needle corresponding to the contact point between the needle and the stop pins below "E" and above "F." This nearly microscopic "v" acted as a friction hold on the needle itself.
Simply slip a bit of very small diameter heat-shrink tubing over each stop pin and hit it with a little heat (a hair dryer will do,) to shrink tightly over the pin. You have just
rubberized the pins. Fixed!