No I'm not saying that. The fuel tube is designed in such a way that is has a upper and lower fuel port. They are separated by a section of the fuel tube that has no screen to allow fuel to flow. When the fuel reaches this level no fuel can flow and you then go on reserve. Once the petcock is turned on reserve it opens another portion of the value that allows fuel to flow, in a sense your petcock has a valve within a valve. IF fuel can leak around this fuel tube O ring it allows fuel to "by-pass" the section of the fuel tube and will simply allow fuel to flow to the carburetor all the time. I found this old image in my photos, look closely at it, you can see a section of the tube that does not have a screen, when fuel reaches this level you should have no fuel flowing if it is working properly and that is when you switch to reserve. All this only works right if the fuel can not leak/flow around this O ring and giving you a false reading and you have a petcock designed to work this way. There are all kinds of Petcocks, this one photoed is from a Transalp and requires a vacuum line to open the valve, you can see the similarity in how the fuel tube mounts, I am merely showing this photo to show the Fuel tube which is identical.