A jumping gas gauge seems to be an issue that quite a number of classic car (from Mustangs and Corvettes to Porches) owners are experiencing. Like me, most are living with it. However, as has been indicated, it is not a gauge problem but the lack of proper gas tank baffling around the sending unit float.
To eliminate this problem, some cars manufacturers have installed their sending unit float in a tube where others have addressed the action at the gauge. When the VW Beetle first provided a gas gauge, they baffled the gauge by used a bimetallic heated element in the gauge. Other manufacturers have created circuitry that would reduce responsiveness by averaging out the sending unit signal over a period of a number of seconds. And still others (United Instruments aftermarket gauges) simply install a thick silicon lubricant to dampen the needle. I believe what Bill is looking forwhat Lin seems to have found, a baffling circuit matched to the Healey's gauge and sender.
Bill, although this seems redundant base upon Lin’s success, I would suggest when you make sure the manufacture specifically states it will handle the Healey’s gauge and sending unit and will provide, or adjust, to giving correct readings throughout the full range. Additionally, check to see that it will handle the initial surge when the care is first turned on with a full tank. I was told condition could cause circuit and gauge burn out.
Hope this helps,
Ray (64BJ8P1)