Hi to Rob, Theo and the List
Several years ago I ran into this same problem. Theo is probably right on
when pointing out the voltage regulator. That was my problem at the time. As
a fix, I used a three lead electronic programmable voltage regulator (LM317)
in a plastic pack. The big advantages are that it has an self protection
internal current limiter of about two Amps (in case of a bad sender or short
somewhere) and it is ambient temperature insensitive. It cost around $3.00
in quantities of one. I ended up building a pair of them, one for the temp
gauge and one for the gas gauge. By using an adjustable potentiometer
(resistor) each one can be set for the exact voltage that the gauge/sender
combination requires to be accurate at ONE setting. (The linearity is
another complete issue that you probably don't want to concern yourself with
at this time.) I calibrated using a separate digital thermometer with a
thermocouple junction slipped up under the top radiator hose into the fluid
as a reference temperature. As I recall, the temperature gauge/sender wanted
a voltage of around 9.5 volts to read the same temperature on both units.
For the gas gauge, I emptied the gas tank (disconnect the hose at the pump
output on flat ground and let it pump till it quits) reconnect the hose and
refill with exactly 2 gallons, and then calibrate the gauge on the 2 gallon
mark (that's where it counts anyway). A full tank reads just under the full
mark on the same gauge.
I live in Arizona and have FlowMasters on my Tiger. In the summer, with a
120 degree ambient temperature and a radiated road heat, it gets real warm
under there. I was concerned with both vapor locking (I have actually
experienced vaporizing the gas in the pump and line) as well as the rubber
hose deterioration. They put a lot of Alcohol in our gas here (Steve,
remember that wonderful gas we got at Big Bear last year???) and as I recall
Alcohol vaporizes somewhere around 140 degrees Fahrenheit (with no pressure)
and a little higher under 5 lbs. of pump pressure. This is still well within
the range of the temperatures experienced around the fuel pump. To make a
long dissertation short. A heat shield helps deflect some of the radiant
heat off the muffler and road surface and helps a bad situation.
Cullen Bennett
Tempe, Arizona USA
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