I haven't gotten that far on maintenance schedule - good catch. Looks like I'll need one at some point.
A quick search for that part number came up "discontinued". http://www.gearhead.com/yamaha-90890-03094-00.html#/s/YAM//90890-03094-00/1
I once owned a Corvair, which had two carbs - the old school way to synch them was to stick a piece of tubing in each ear, and into the throat of the carbs - you could 'hear' when the carbs were synch'd. It actually worked pretty well, although a backfire could be bad for your ears.
What we're talking about here is a basic manometer. With some ingenuity, a couple of pieces of clear tubing and a jar of colored water, you could make one. Motion Pro makes good quality stuff, not sure about Carbtune Pro. Local shop guy has the Motion Pro that he said he never uses, so I may be getting a deal....