Tigg found this article on the hyper charger that explains it well.

Kuryakyn Hyper-Chargers

Now here is an interesting item. It is possibly the most popular after market 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 operate off manifold vacuum and the top fuelers are operated mechanically by the throttle linkage.

http://www.harleyhelp.com/hyperc05.gif

At idle and normal cruising speeds, the main air intake is through the open butterflies, but when you accelerate, opening the carburetor or throttle body butterfly - the manifold vacuum drops causing the Hyper-Charger's butterflies to close. Now the main 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 theHyper-Charger body for this purpose.

http://www.harleyhelp.com/hyperc06.gif

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.


http://www.harleyhelp.com/hyperc07.gif

Because of the way the air travels into the front and out the rear of the Hyper-Charger, instead of forcing air into the carburetor, it actually pulls or "siphons" air (and fuel) out. 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.


Source: harleyhelp.com

thanks for the info , i was just gettin ready to drop the cash for this unit.

so is there any way to have the hyper charger and not get the drip b/c i have been looking at them and i havnt heard this til now i would like to know what is preferred for a sporty 1200 if the hyper charger is a bad idea

I've got a Kuryakin Hypercharger.
I've never had it drip on my boot, my pipes or my garage floor.
http://www.hdtalking.com/harley_gallery/data/545/medium/hypercharger.jpg

It gives me plenty of power at highway speeds.
The mechanical flapper generally closes at anything less than full throttle and air is sucked in the lower opening just like other high flow air cleaner boxes.
If you're full throttle on the highway all day you're braver than me! If the throttle body was creating enough suction to pull fuel out into the Hypercharger you wouldn't just lose power, you'd stall. It just doesn't happen.
try blowing air over the top of an open Coke bottle and cause the soda to fly out. Use an air hose if you want. Now put a K&N air filter sealed tight across the opening. It just can't create the kind of suction necessary to create a vacuum in the bottle.
Oh yeah. I've been on long rides with this set-up. 2000 miles in 4 days long enough. Not a hint of oil or fuel in my Hypercharger or anywhere on my bike, boots, chaps, luggage or route 66.
To post personal observations or scientific studies is of great use in forums like this.
To post bad science as gospel for all to read and reject a product outright is possibly slanderous.
I have a lot of respect for Glider. He posted this with good intentions and attributed the source. Investigate for yourself if the source is qualified to hypothesize about the science involved. And ask what experiments they have conducted to prove said hypothesis.

I would take the suggestion that they are ineffective or cause drips with a grain of salt.
Preferably followed by Tequila and lime!

Had 26,000 miles on my springer when I sold it and had the hypercharger on it. Never a drip, never a problem. (shrug)

thanks for the info i am glad to here all of that before i spent the money thanks again

No body ever said the article was gospel . It was just something to think about. Your coke bottle analogy is flawed because the coke in the bottle is not a mist or being sucked into an open area like the fuel in the venturi of the carb is .In a carb the fuel is aready being "sucked "out of the fuel bowl by passing air through a tapered orfice . If the fuel can be sucked out of the carb to the cylnder then why isn't it feasible that by creating a greater vaccume at the opening of the venturi of the carb (or fuel injection unit as long as it is a throttle body type and not direct injection) that the fuel could not be redirected or at the very least "slowed down" causing a lag or bog at highway speeds. A sandblaster uses a syphon tube in much the same fashion. By passing air ah a high velocity over a syphon tube the sand is sucked up and expelled with the air passing over it. I am not by any means saying that the Hypercharger isn't everything that it is advertised to be I am just saying that the info in the article makes enough sense to make you go HUMMMMM. Just my 2 cents

Excellent post Tigg!

Makes more sense when you put it that way.

Your coke bottle analogy is flawed because the coke in the bottle is not a mist or being sucked into an open area like the fuel in the venturi of the carb is ...

I agree that my Coke in a bottle analogy is full of air.. Never been great at analogies.:bigsmiley30:

But see how much sand your sandblaster sucks up if you put an air filter in the way to disrupt the speed of the air and any potential "suction". Oh yeah and close the air intake like the butterfly on my Hypercharger closes.

Don't want to argue. I just hate to see a good product slammed for what is an unproven theory. Talk to those who have one. That's what this forum is about.:kissyou

I understand your point but there is already enough air flow throught the filter and hypercharger to create a vacuum or the bike wouldn't run. By opening the butterflies and drasticaly increasing the air flow you would be creating a venturi effect around the air filter. Fuel might be sucked away from the cylinders between the opening of the intake valves. This is why the Harley systems use a cover that completly sheilds the air filter. to stop the Syphon effect.Also if the butterflies are closed wouldn't that make it a very inefficient system because of the limited air flow through the small port on the bottom of the hypercharger when you need it most. the stock airbox has larger openings that the Hypercharger bottom.