Motorcycle Repair: stalling when fuel valve on On position, suzuki savage, resever

Question
2000 suzuki Savage 1 cylinder 650. In on position after a while or sputters and a a stop stall doesn't seem to grab gas. In resever or Prime position runs ok. Have replaced spark plug to try to remedy. Have stored for winter with stabilizer in tank as well.

Answer
Moe.... are we talking about a bike with a full tank of fuel? Prime or Reserve drains the last bit of fuel, while the ON position quits when there is about 1/2 to 1 gallon left.. see your owner's manual.
If this is happening with a full tank, then you have some restriction in the fuel petcock, perhaps. Flush the tank, petcock and drain the carburetor bowl and refill with fresh fuel.

Bill Silver