Starlight Sniper, per the official errata for Axis and Allies 1914:
“While it remains neutral, the United States is not considered to be either friend or enemy to any other power, and it may not move land or air units out of the United States of America (including onto transports) or attack Central Powers sea units.”
Since it is very unwise for Germany to bring the US into the war early (unless you are playing with house ruled unrestricted submarine warfare rules), the US will not be in the war until its 4th turn. Per the quote above, the US cannot load transports until its 4th turn (or whenever it can declare war) so the US cannot reach Istanbul with loaded transports until US turn 6 in pretty much every game.
On the bright side, the US is completely unnecessary in a KTF strategy. The British should just spend all of their income in India (except maybe a transport or 2 in the Atlantic). If they do this they will have the Ottomans turtled in Istanbul by turn 7 or so and can begin the assault sometime around turn 8-9. I doubt that the US troops could do very much to the Ottomans other than maybe force them back to Constantinople a turn earlier.
ColonelKurtz: Using just the OOB rules and the official FAQ, my experience has been that a full KTF with Britain is the simplest path to a win for the Entente. It is my opinion that the simplest way to balance the game (without any really crazy rule changes) is to find a way of forcing the UK to spend in the Atlantic rather than 100% in India.