Bike not getting fuel when in the on position at the fuel ****.

Fuel petcock position depends entirely on what you're doing with your bike at the time.

In normal use, the fuel petcock should be set to the "on" position and left there. In that position, gasoline will be drawn from the tank only when the engine is running and generating vacuum. This prevents overfilling the carbs when the bike sits.

When you're riding the bike and it starts to sputter, it's time to move the petcock to the "reserve" position so that you can use the last few drops in the tank (on a 650 special, this was either .3 or .5 gallons--can't remember which off the top of my head) to nurse your bike to a gas station. Once you've filled the tank, move the petcock back to "on." The bike will still run fine if you keep the petcock in the reserve position, but when it starts to run low on gas--well, you won't have that emergency reserve to get yourself to the gas station.

If you've managed to run the bike out of gas completely, or if you are getting the bike ready for service after having drained the carbs for the winter, you'll need to move the petcock to the "prime" position for a few minutes. This by-passes the vacuum line cutoff mechanism and lets gasoline flow until the carb floats shut off the fuel valve (this is also how all older motorcycle fuel petcocks operated). A sticky float or poorly sealing float valve in the carb can, however, cause far too much gasoline to drain into the carbs (and into the crankcase, if you're particularly unlucky), which is why you should not leave the petcock in the prime position for an extended period of time.

Some Yamaha XS650 motorcycles (can't tell if that's the model you have) have a tank with two fuel petcocks, one on each side, to fuel each carb. If you have a tank with this setup, be aware that setting one fuel petcock to "prime" will affect both cylinders, as there's a crossover tube to equalize fuel levels between the carbs. Also, for reasons I could never figure out, on one XS650 I owned, moving either petcock to "prime" permitted fuel to flow on a gravity feed out of both petcocks simultaneously. I could never figure out exactly why it was doing that.

Check carbs for old gas deposits ussually when gas sits for a while it turns to varnish and it can plug small hoses and lock up small moving parts like floats for example. next time you store the bike for the winter, close the gas shut off and run it till it empties the carburators. Im not a mechanic but I stayed at the Hilton once. Good luck

dont move the needle position, hopefully you drained all the old gas, get a can of carb cleaner at the parts store,remove bowl plug under carbs stick nozzle up and spray, should be a idle adjustment screw under carbs turn 1/2 turn, also when you go to to the parts store get a can of fuel injector cleaner and marvel myster oil and put in tank. then take bike for a nice long ride

loose wires seem to be a big thing with these bikes wiring diagrames is available online try google images if i get chance il add a link later

as for fuel problem turn the fuel tap to 3 oclock position prime constant fuel feed if you get it running this way turn tap on position down

most people including myself have had problems with bike only running on 2 cylinders usually 1 + 4 ive cleaned the carbs fully and replaced coils and leads + plugs also cleaned every connection and made them tighter with pliers etc to all wires under the tank as on my bike was all gummed up oil + corrosion etc bike now runs alot better

The On position is where you run the bike after filling the tank. The Res position is when you are almost out of fuel and the motor stutters you turn the switch it it and that will give you about 1/2 a gallon of gas left in the tank to get to a gas station and refill. Pri is for priming the carbs only. If you have ran out of gas after using the reserve fuel you switch it to this position to fill the float bowls with fuel. Do this for only 30 seconds and switch it back to On position.

Is your bike fuel injected or carbureted? If it is fuel injected the tank has a 4.5 gallon tank and that's it. If it is carbureted the fuel petcock is a three position valve (ON, OFF, RES), the valve is configured in the tank where ON allows fuel to flow until you are down to about 1/2 a gallon at which time you would turn the petcock to RES which allows the engine to use the last 1/2 gallon of fuel and gives you time to hunt down a gas station.

There is no separate "reserve" fuel tank.

there is only one tank to fill on your bike, your getting confused by the reserve. The reserve is just on the fuel tap itself. It has three positions, on , off and reserve. In the on position your fuel tap will be able to drink about 90% of your fuel tank and then it wont be able to drain anymore, then you must turn your fuel tap to the reserve position and it will be able to drink rest of your tank approx 10% that is left. So next time you fill up at a petrol station make sure your fuel tap is set to on, then when your bike starts to splutter out of fuel you can turn your fuel tap to reserve and get yourself to the petrol station to fill up, making sure you then turn your tap to on again. If you keep running out on the reserve it can cause debris in your tank to clog your carb up.
hope this helps
steve

Check the vacuum pipe from the carbs to the fuel tap, if its gat a pin hole in as you demand more fuel the vacuum loss cuts downthe fuel flow and the bike will stop!

how long ago did you check the engine valves clerance ? if longer than 30000km ago it can be the problem...sorry for my english...it's weak

sounds like you may have more than one problem. as far as the fuel......the prime position allows gas to flow continuous without the need of the fuel pump. as far as the 11 volts is that with the key on or off? what are the volts at the battery terminal?