The reserve is part of the main tank. It is just the position of the petcock that determines if you are pulling from the "reserve" part of the tank.
AAHH...this is your first tank of gas through the bike? The dealer should have told you how far the bike can go on a tank of gas. Give it another tank (with the reserve turned off) and when the bike starts to sputter, flip to reserve and see if it still runs out of fuel. Again, you only have 20-30 miles until the tank is dry. If it still doesn't run right after you turn it to reserve, take it back to the dealer and ask them to fix the problem with the petcock.