Kuryakyn Hyper-Chargers

Now here is an interesting item. It is possibly the most popular aftermarket product for sale, and yet could be the cause of a lot of the problems I have been hearing about.

Let's start with something you might not have noticed. One of the most attractive things about the Hyper-Charger are those cute little butterflies that flutter open and closed when you work the throttle. It's so cool, just like the blowers on the top fuel funny cars... except for one thing, the Hyper-Charger butterflies are spring loaded open and close by high manifold vacuum and the top fuelers are operated mechanically by the throttle linkage.
(Actually you can disassemble the Hyper-Charger butterfly assembly and reverse them to be spring loaded closed and open on vacuum)

  At idle, the throttle plate is closed and manifold vacuum is high, causing the Hyper-Charger's butterflies to close (partially).  The front air intake is shut off by the closed butterflies so there has to be another air intake area, and you will see a slot at the bottom rear of the Hyper-Charger body for this purpose. At cruising speeds and under acceleration the throttle plate is open. resulting in a low manifold vacuum the main air intake is through the open front butterflies.

Kuryakyn claims that installing this air cleaner kit will improve performance and horsepower and that is true... under the right conditions. The reason it improves performance is because it utilizes a K&N free-flowing style filter, the same as you will find in the Screaming Eagle air cleaner kit and many others, even S&S is using the K&N style filter now. What the company does not tell you is that it will produce much better results on the dyno than on the highway. On the dyno it works great, but the dyno won't reproduce that 80mph wind forced into this air cleaner and out the rear like you get on the highway.
Because of the way the air travels into the front and out the rear of the Hyper-Charger (no matter if the butterflies are open or closed), instead of forcing air into the carburetor, it actually pulls or "siphons" air (and fuel) out. This is how vacuum is created, air flowing across a perpendicular opening will pull or vacuum from that opening. As a result, you get what has been described as a "dead spot" or lack of power at highway speeds, not to mention the fuel breaks down the oil in your air filter hampering it's usefulness and the fuel mixed with air filter oil tends to deposit itself all over the right side of your bike when you go on long rides and then when you stop it all drips down on the cam cover, your foot, that cigarette butt you just dropped, and so on...