I agree that it sounds like what ual767 is saying. But if the engine is sideways, and the tank center line is pretty close to being in line with the spraybar, then it's something else.

But the basic problem of the mixture leaning, I think, is right on. So, the question becomes why is the idle leaning as you idle down.

Another possibility is that there is an air leak in the carb or carb mount area. This would allow too much air in, and cause the engine to not draw fuel like it should at idle.

Just to clarify, it sounds like the engine idles a bit fast, but is stable, and transitions to higher throttle settings fine? If that's the case, then I'd probibly just reset your throttle linkage to allow the barrel to close fully, and go with it.

Also, on any engine, but espeically ringed engines (as the 1.08 is), the idle can take a long time to really settle down. If you only have a few tanks though, I wouldn't sweat idle oddities right now.