Clear this up for me once and for all please. So when one switches over to fuel reserve, there is an internal valve that transfers to a lower section in the fuel tank in order to draw remaining fuel? I'm trying to visualize otherwise i.e. if you were to fill up at the pump with a completely empty tank, where does the fuel go, to two different compartments, or just one main tank? I've never tried or forgotten to move the petcock back to main after a being bone dry and filling up. But would you only be able to go a short distance utilizing only a reserve compartment? I know I've heard not to forget switching back to main after refueling or there just won't be any reserve, so I'm confused on the internal workings.

 

there are two holes in the petcock, the main has a longer tube. my reserve has no tube.
http://w6rec.com/duane/bmw/petcock/petcock13A.jpg

 

Attached above the petcock there are 2 tubes standing up into the tank. The tubes are of different lengths.one is taller than the other. When the lever is in the on position the fuel is taken into the taller tube. As the fuel gets used and the level drops, the taller tube becomes uncovered and the fuel doesn't go into it. This is when we would go to reserve and the lower tube will allow the remaining fuel in. Ya won't ever have a completely dry tank but it'll be close. Not a 2 compartment tank but the petcock has 2 ways of allowing fuel through it.

Hope this helps WP

 

nicely said WP50.

 

ok…so when someone says you just won't have any reserve….what they really mean is there will be no warning, when you're out, you're out. Clear pic in my noggin now WP, thanks

 

Your 2 pics probably helped as much as anything Sir.
I'm an early riser but not usually thinking and typing that much

WP

 

Your Welcome Sir

WP

 

Sounds cool.

 

This thread actually was useful looking back at my sporty it didn't have the two tubes only the longer one. So hypothetical speaking you take the smaller one out you would get more out of the reserve?

 

The reason even the reserve tube leaves a smidge of unreachable fuel in the bottom of the tank is that it gives a place for sediment/gunk to settle.

Or so I was told.