In this video, Terry Blow shows the carburetor screw locations. If you are feeling impatient, fast forward to the 10 minute mark.
http://www.youtube.com/watch?v=eZP3xZVgl-I
If I may expand on what maniac57 said,
The slow speed mixture screw on the HuaSheng is a fuel adjusting screw. Turning the screw in (twisting it clockwise) closes off the passage that the fuel flows through. This will reduce the fuel flow and lean the fuel/ air ratio.
Turning the screw out (twisting it counterclockwise) opens up the passage that the fuel flows through. This will add more fuel flow and enrichen the fuel/ air ratio.
This screw has very fine threads on it to allow precise tuning of the air/ fuel ratio.
This screw should never, EVER be turned in and tightened because doing so will ruin the delicate fuel passage inside the carburetor. There is nothing to be afraid of while adjusting this screw if when turning the screw in, you are gentle and stop turning it if you feel it hit bottom ( stop turning easily).
1. Turn the idle
mixture screw in until it bottoms.
2. Turn the idle
mixture screw out 1 and 1/2 full turns.
This gives you a good starting point to begin the tuning process. The engine will run, poorly, but still run.
3. Start the engine and adjust the idle
speed screw in to raise the idle speed or out to lower the idle speed until the engine is running at a fast idle.
4. Turn the idle
mixture screw out until the idle speed begins to slow.
5. Take a mental note of the idle
mixture screw's screwdriver slot position. This slot is the only indicator (pointer) the screw has to visually measure how much you are turning it.
6. While counting how many turns you twist it, turn the idle
mixture screw in until the engine run faster and then begins to run slower again. Stop turning it before the engine totally dies from a lack of fuel.
The number of turns in you made now needs to be divided in half.
For the sake of discussion let's just assume that you turned it in 4 and 1/2 turns.
Half of that would be 2 and 1/8 turns.
Remember, your actual number of turns will most likely be different than the above example so do your own math from the turn count you have.
7. Turn the idle
mixture screw out that number of turns that your math came up with.
Add 1/8 turn more to the turn count to give a teeny bit more fuel into the engine. It is better to be a teeny bit rich than too lean.
8. Now adjust the idle
speed screw in or out until the engine idles at a good speed. Not so fast that the clutch is trying to grab, not so slow that the engine is struggling to keep running.
As the engine puts on miles and breaks in both the idle mixture and idle speed will need to be fine tuned again as the engine's needs will change as it matures. Eventually the engine will be settled in and the slow speed tuning will be good for a very long time.