Fuel gauges work by measuring the current through the sender. The sender is only a vairable resistor, low resistance at full and high resistance at empty. At low resistance you have high current flowing, at high resistance you have low current flowing. I have never seen what the sender on a 140 series looks like, but is it possible you've installed it the wrong way round relative to the float? The mechanism will still work, but (if it's possible) the vairable resistor will operate in the opposite direction and thus the gauge will show your credit card ballance...