Calibrating the tank

Most older motorcycles do not have a fuel gauge. My BMW K75 has only a low level alarm (even older motorcycles have a secondary fuel pickup. When the fuel level goes below the primary pickup the engine sputters and you switch on the secondary and find a gas station, this is the “petcock” valve.)  After seven years of ownership I had finally gotten really sick of not know exactly how far I could go once that light came on.  So I decided to do something about it.

This is not a new thing, just something I had avoided for a long time: run the bike out of gas.  So, I waited until I had about 150 miles on the current tank and found a gas can. I rode down to the local Stop and Rob and carefully put 2.000 gallons into the gas can and put the can in my pannier.

Then I rode. And rode…finally the red light came on and I noted the trip odometer reading.  Then I kept riding until putt putt putt, it ran out of gas at exactly 40 miles after the warning light came in. That was much farther than I originally thought.  I emptied the 2.000 gallons from the can into the tank and rode to the nearest gas station, which it turned out was only two miles away.  I then added 3.3 gallon to get to my normal fill up level.  So I found out that I can go 40 miles on the light, and that I have 5.3 usable gallons of fuel.

I typically get about 45MPG on my commute which means I can get 230 miles or so out of a tank.  I have very rarely gone more than 175 on a tank because I had no idea how far I could go on the light but knew it came on at about 190 into the tank.  So this is mostly a peace-of-mind exercise, but one that should be done on any motorcycle so that you really know how far you can push it before you’ll have to push it.

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