reserve or not to reserve

[mojitomax]

how does the reserve switch on a bike work? the reason i ask is that my daily commute is a 100mile round trip. i reckon i can get about 180 miles from the main tank (18litres) and the reserve tank is 3.4 litres.

my question is if i leave the switch to the reserve position, will the fuel be taken from the main tank and then when it's empty automatically be taken from the reserve tank? or are there two separated tanks with a common filler pipe, so fuel will only be taken from either the main or reserve tank individually?

i figured that if it's the former, then i can get two days before filling rather than having to fill up every day.

Ta for your help

[Glade]

(My current bike doesn't have a fuel tap so i could be wrong but i think this is how it goes)

There is only one tank but it has two petrol feeds. The main feed is higher than the reserve feed. When you "run out" of fuel, you switch the tap to reserve, which takes the remaining fuel from the bottom of the tank.

So an 18 litre tank with a 3.5 litre reserve will use 14.5 litres before it runs out the first time.

If you leave the tap on reserve, when it conks out, you realise, swear a bit, then start pushing!

[black-k1]

How it works:

There will only be one tank. The main fuel feed will have a length of pipe on it that will mean the last 3 to 4 litres are left in the tank when main feed runs dry. The tap is then switched over to the reserve feed which is set lower in the tank thus gets the remains of the fuel. (Simple diagram below shows fuel level after switching to reserve.) You can run on reserve all the time and it will just empty the tank in the normal way but, when you do run dry, there is nothing left! This can be a problem when you expect to get a certain mileage out of your tank but forget about the 50 miles of ‘hooning’ you did when you filled up. The extra fuel used at the start of the tank may just leave you with a couple of mile push to the next garage! (been there, done that!)

Main feed

|  |    
|  |
|  |~~~~~~~~ Fuel Level ~~~~~~
|  |
|  |
|  |     Reserve feed
|  |
|  |         |  |
|  +---------+  |
|      Tap      |
+------+  +-----+
       |  |
       |  |

[mojitomax]

Ah, that's what i thought, but i just wanted to make sure. another thought has just occured to me though. in the manual, it says that the tank capacity is 18.0 litres and the reserve amount is 3.4 litres. does that mean that there is 18 litres in the main tank + an additional 3.4 litres reserve or that there is 14.6 in the main tank and 3.4 reserve = 18 total?

i'm inclined to think it's the latter which may have made this whole dicussion a bit of a moot point

[black-k1]

It doesn't really make any difference as you are unlikely to be able to get all the fuel out of the tank anyway. The only way to find the tank capacity is to run it until it's dry then measure what you put in. That, and that alone, is you usable tank capacity.

[mojitomax]

ok, i've checked my fuel receipts (need to keep them to claim back the costs - i'm not just crazily anal!)

after running out and switching to empty, i put 18.8 litres in the tank. so does that mean that the reserve tank of 3.4 litres is in ADDITION to the stated capacity of 18 litres of the main tank?

[Hooli]

tanks will hold more than the spec says, because they have to build in an airgap. shake it a bit as you get to the top when your filling & you can fill past the filler neck & hence into the airgap. at thats how it works on the two ive had as the filler neck extends down into the tank about 1/2".

ive managed 22.73ltrs in a 22ltr tank before & it was still running when i pulled up at the pump. i know for a fact it wouldnt restart that low though.

[sjtscott]

I only ever had a reserve switch on my first bike 97 zx6r to be honest you needed it on that bike as you had no fuel light or guage and just a trip counter. I remember many times trying to learn to switch it over as it started to run dry on the main tank while riding along. I always kept it on the main setting and really only used the reserve for the odd occasion.

All my other bikes have had fuel lights and on some reserve trip counters or count down reserve markers. Trip counter for me is still key as I effectively know when the bike will switch to reserve. Generally when the bike hits the effective reserve bit I always try to fill it up ASAP.

[TallPaul]

Some unscrupulous petrol stations may also be selling short measures, meaning you paid for 18.4litres, but in reality, you got 17.4litres. Obviously, this is highly illegal, so I'm sure no garage would ever do this.

[sammy_bibs]

Found this,

A common misconception among new riders is that there is a "reserve tank" on a motorcycle which is actually a separate tank from the main tank. Some also worry that the reserve tank might run out of gas independent of the main tank, but they can't figure out how to fill it.



The blue area is the "fuel reserve." The red area is unusable fuel. The white area above the blue, inside the tank, is the "normal" fuel.

---

That first paragraph is highly amusing, 'worry that the reserve tank might run out, can't figure out how to fill it' =)