1999 nija zx6r. should the lever be in the reserve or on mode when riding on a full tank of gas.

Check the reserve fuel line and the main fuel line to make sure they haven't been switched. I purchased a Suzuki Intruder and was riding all the way to reserve to check the mileage and when I ran out I couldn't start it even though I switched to reserve. Turns out that someone had the tank off to service the air cleaner and had reversed the two fuel lines so the fuel valve was running the bike on the reserve tank tube. so when I switched to the reserve position it was hooked to the taller brass tube in the tank and the gas level was already below it. The tanks just have two brass tubes, one taller than another so gas cannot be sucked below the taller tube when on main and then when switched to reserve it sucks from the shorter tube allowing the remaining gas to be used.

Hi Kumud:
On my KLR 650 the reserve is 0.9 US gallons.
There's really not much point in worrying about "non usable" amount.
What I would recommend, especially if you're going to do any remote riding, is to strap a spare gallon (or 2) to your bike, then go for a ride. When you run out of gas, reset the trip meter to zero, turn on your reserve, and ride until you run out of gas again.
You will now know how far you can go on your reserve. That's the first important part.
Now put you spare gas into the tank and ride off to find a fuel station. Fill the tank, set the trip meter to zero, make sure the fuel selector is set to "ON", and go for a ride until you run out of gas again.
You will now know how far you can go on a full tank before you have to rely on the reserve.
If you use this system it won't matter what machine you have, and depending on your riding technique, the distances will vary.
Gotta love riding!
cheers.

Sounds like the reserve lever on the petcock is not being used, Your petcock should have 3 positions, OFF , ON , RESERVE. Learn how to operate it!!
Reserve will allow you to run a few more miles to get to a gas station!!

Are you turning the tap the right way as it sounds like you are running on the reserve tank all the time and when you turn over the tank is already empty.

You dont ...

Several things for your consideration.

You should be able to ride for about 100 miles on a full tank. Fill up every 100 miles.

There should be a three way valve on your tank; OFF - ON - RESERVE. NEVER set this to RESERVE unless you miss the 100 mile fill up. Otherwise, you will be walking.

You may be able to go 150 miles on a tank ... DONT DO IT. @ 90 miles, start looking for a station where you can fill up. Your pututti will also thank you.

With the age of your machine , you should drain the tank and remove the petcock. If you can take it apart rebuild it. If you have no reserve , either the reserve tube is broken off or the petcock is plugged. It is possible the four hole washer the seals the the lever and diverts the fuel is damaged , worn , or broken. Depending on the over all condition of the petcock replacement of the entire unit may be the best option. At any rate an new fuel petcock would definitely fix this issue. Rebuilding your old petcock is only an option if all the parts you need for it are available.

When you have it on main there is a little pipe that sticks higher up into the gas tank and once the gas get down below the top of the pipe it will start to make the engine sputter and you have to flip the lever over to reserve so the rest of the gas can be used. But once you have used up all the gas in the tank you will be empty. So when ever you flip it to reserve you will only have about a 1/2 gallon of gas left to get you to a gas station to get it filled back up. No there is not a separate tank in side the main tank.

The valve is open when the lever and valve are parallel. Generally that is down. When the lever is pointing across the valve it is closed. Think T vs. I. If the lever and valve cross it's closed, if they go the same way it's open.

That applies to a two position valve, if your Bayou has a reserve postion it could be different. That would be three positions and across one way would be open, down would be reserve, and across the other way would be closed. Should be marked on the petcock if that is the case.