Awesome Alt. to Airbox to Carb Boots

That you could tell, anyway.

My thinking is this: Yamaha went to a lot of trouble, engineering-wise, to craft the inner profile of those boots in the complex shape that they are. Yamaha generally didn't do things for no good reason. How much of a difference it makes, and under what conditions, can be debated; but Yamaha made them that way for a reason.

 

The airbox boots on my 700 were straight thru. I'm thinking that since the airboxes are all the same size, that smaller carb/engine models may have boots that taper as Fitz is talking about? I'm guessing it's just how they are fitted to the smaller carb and that the taper is too slight to make a difference.
After all, the boots were made to channel smooth airflow to the carbs, not accelerate the flow. At least that's the point where my thinking arrived.

 

I've just looked at a 900RK boot that the dog brought in (clever boy!) and it's not especially complex as regards shape apart from the velocity-stack shaping of the ends of them, nothing special... Until you realise that they're actually shaped so that the 2 left & 2 right side boots face away from each other by a few degrees, presumably to combat charge robbing?

I don't think Yamaha spent a vast amount of time or money on the actual shape of them to be honest, they're just a velocity stack. Where they spent the time (presumably because they found they had to, for whatever reason) was on that "splayed" angle of them...

Cleverly they saved money by only making one boot per carb-size though, and then just located the lugs on the airbox top one side & bottom the other to make them angle differently between left & right 8)