is there anyone who knows which tank this is and if there is fuel

reserve in it , I do have a reserve position on my petcock .... but you never know

 

"Reserve" is created by 2 vertical tubes of differing heights on the petcock itself
It`s not a "compartment" inside the tank
No idea who made that tank

 

Don't know the brand of the tank, but somebody will recognize it.

The reserve is usually a feature of the petcock and NOT the tank.

The petcock has two inlets (or ports) to the fuel line (over simplification). One of those inlets has a standoff tube attached. When in "normal" position, fuel flows into this standoff tube until it ultimately reaches the level of the stand off tube and then you "run out of fuel".

You switch over to "reserve" (you are actually moving or aligning up ports in the petcock-like a switching valve) and you are now drawing fuel from a lower standoff or port than the original normal tube. You are now on reserve. It is just a simple way of telling you "you have about xx amount of fuel left before you completely empty the tank".

While not precise because the fuel in the tank sloshes or moves around, but it's a close enough kind of thing.

Knowing about how many miles/range (or how much fuel is still left in the tank when switching to reserve) is a nice thing to know. You can make a pretty good guess by starting with a completely empty fuel tank, and a clear fuel line going into a gas can from the petcock, normal lever position of the petcock, bike as close to straight up as practical, add fuel to the tank until fuel starts to flow out the petcock. When your adding fuel to the tank and the petcock just now starts to flow at the 1.5 gallon mark, then you have a 1.25 gallon reserve. Yep, I said 1.25 gallon reserve. That keeps you out of trouble even if it is actually 1.5 gallons...trust me...Also knowing your bike MPG's and watching your odometer is a good thing.

Another old school last ditch effort to squeeze another few miles out of the tank is leaning the bike way over towards the petcock side of the bike. There is always residual fuel in the tank, and usually a tunnel or hump in the middle of that tank, so leaning will move a little more of the residual fuel to the petcock side of the tunnel (hump) and may be just enough to get home, gas station, etc. Sure beats pushing or walking when you used up all the "reserve".

Not a harley petcock, but you get the idea, taller tube is "normal", shorter is "reserve".

 

Thank you very much.

Then a small question, how do you do it to remember how many mls / kms you have refueled to know what is left in the tank, I only have a km counter without a reset button ?

 

Each tank/petcock combo has it's own level of "reserve." You just have to ride until it cuts out, hopefully not when passing a truck, etc., switch to reserve and note how far that was from fillup.

 

Pen and paper write it down. Long as you are not in the middle of no where ride until it sputters and is running out of fuel . Switch the reserve and hit the first gas station.
However you need to know your bike and riding habits . How long you get from reserve will very from model to model .
In your case with a custom tank you will have no idea until you test it a few time. if you are on the way home and switch to reserve fuel right away.
It sucks to get up take off on a ride and run out of gas. reach down to use reserve and find you already did..

 

Short answer. Figure out you average kilometers per gallon, liter, etc.

Then keep track of kilometers travelled, and estimate at what kilometers (number) you should start looking for fuel.

4 gallon tank at 50 miles per gallon is 200 miles. If reserve kicks in at 150 miles, then you used 3 gallons and you have 1 gallon left (theoretically). There are variances in driving habits, wind, hills, traffic, etc.

So for me, I would be looking for fuel at about 125 miles travelled. This of course is just an example.

If 1000 miles on the odometer, I fill up, and note to self at 1125 miles I need to start looking for fuel.

 

With the bike straight up as you can safely get it, put a long hose on the petcock, turn it "on" and drain it.

Use a separate container, turn petcock to reserve. Measure that, and subtract about 20% (they'll quit running sooner than the gas is totally drained)

Fill the tank, go ride. Fill again after 100km or so and check fuel mileage. Do the math and that will give you a close guess of available distance per fuel unit with the "reserve" position. Always assume you'll get less distance than expected on "reserve"

 

Not that easy with a vacum operated petcock.

I had to use an old syringe (without the needle) and connect it to the vacum pipe on the petcock.

And with the syringe pulled out I made enough low pressure to open the flow of gas.
I guess there are smarter ways, but I could not think of one at the time...

 

Looks like the OP has a manual petcock, but great idea on a syringe to open a vacuum version, especially if one doesn't have a hand pump and probably easier to use anyway. Syringe never crossed my mind...