Hi Kev,
I assume you mean the mechanical system, like the K-jetronic etc.
They are pretty finely balanced, and I suspect that the unit will have to be vertical, as you may find that it does not sit properly at the idle position, and that there may be more friction affecting the movement.
You will have no doubt gone through the same thought process as me and I think that the only way to find out would be to lay a unit on it's side and see if the paddle changes position.
Not a lot of help really, but I thought someone should have a go at answering the question.
