Fuel Reserve / Gauge

[Selby]

How closely does the fuel gauge match the gas in the tank? I was riding yesterday and the gauge reached the red. When I stopped and filled the tank, it would only take 3.3 gallons. Is my gauge off, or is this typical? When do I need to switch to reserve?

[Meikol2]

You will find the fuel gauge to be inacurate. Mine is in the red at 2.5 gallons below full. A much better indicator will be your mileage from your trip odometer. You will have to get to know your bikes set up and mileage for that though. If your bike starts to sputter and die, switch to reserve and go get some gas.

The tank is all one container, but the "reserve" and "on" setting allow fuel to enter the part of the petcock that is in your tank, at different levels (think of it as a tube with two holes in it, with the switch covering one hole or the other). Use the "on" and leave the reserve until you need it, that will save you from running out of gas completely and getting stranded.

One other note. The "prime" setting just eliminates the need for the engine to be running to flow fuel. Otherwise vaccum created by the carbureators causes the valve to flow fuel only while running.

[md86]

Just run it till you need reserve , then note on the gauge where reserve becomes necesarry . First time I hit reserve on mine the gauge had JUST reached the red , so now when I'm close to that , I know it's about reserve time , and eventually time to fill up .

[Black_peter]

I've been thinking about this. Mine took about 3 gal. while in the red. There is a float inside the tank, attached to an arm. The arm is connected to a variable resistor. As the arm moves (float goes up and down based on fuel level) the resistance changes. Current passes through the resistor and is displayed by the "gas" gauge. Lots of factors can effect this. Pinholes in the float, The arm being tweeked by dumping the bike, rough handling of the tank or replacement. Meikol2 gave a good discription of the fuel cock. If the tank is reading low (redline with 2+ gal left) be thankful.
I was stranded once by a bike with a .0005 gal reserve. My old Honda had about a days worth of gas in the reserve. This one had 5 min.. Long story.
Anyway, I would not try and adjust this as you could make it worse. I have been wondering if it is worth devising an "adjustor" to correct inacuracy.
But is it really worth it? Motorcycles lasted about 80 years with out fuel gauges. Some have eliminated "reserve" in favor of trusting the gauge in my opinion the second greatest sin in motorcycle "advancement"..