Re: km not so good
I'll hop in here an add to this discussion since Im finally smoking out of a KM now. I own a 22" Mya Acrylic, a 26" Chinese 2-Hose, and a 34" KM Classic. Out of all three, the best two smokes come from the Mya and the KM.
A few things to watch out for though :
The KMs have probably the most free draw I've ever experienced on any pipe I've smoked. If you chain hit off them, you will burn your shisha unless you're using a very small amount of coal. Try changing your method to taking a draw once every 20-30 seconds.
As others have said, make sure you've got your bowl packed low enough that the moassel isnt touching the foil. Regarless of how much heat you have, if you've got the coals touching the tobacco, it will burn and taste like shit.
Adjust the water level in your base. You'll get a harsher smoke if you dont have enough water for filtration. Ideally the water should be 1" to 1-1/2" above the bottom of the stem.
Add a diffuser if you want to smooth out your smoke a bit more. It will add a bit of resistance to your pull, but the smaller bubbles create more contact area with the water, cooling the smoke more than without. A diffuser will also lower the amount of vibration you get while smoking, and in turn cause less ash to fall through the foil into the bowl. If your bowl gets filled with ash, its going to taste bad as well.
Above all, make sure you're smoking decent moassel. Theres tons of reviews to check out and you'll find most brands such as Nakhla, Starbuzz, Al Fakher, and Tangiers are held in high regard around here depending on personal tastes.