the bike doesn't turn at all
If you are having a complete turning failure, the reason is more likely to be controller position than anything else. The wii-mote uses gravity to detect wheel position. Straight (neutral) wheel position has the top, bottom and face of the controller in the horizontal plane with the long sides facing skyward and groundward. From this position, rotate the top and bottom around the middle to turn, the face should continue to point toward the horizon. Maximum turn appears to be at 90 degrees, but 180 degrees (all the way over) is allowed - a significant amount of over-turning is permitted.
If the face of the wii-mote is pointed skyward or groundward, it will be unable to register any turning motion.
Now, on to drifting... Drifting requires a few things:
- Sufficient speed - too slow and a drift will not begin. If speed is lost during a drift (as sometimes happens with collision), the drift may terminate unexpectedly. Collision by itself does not terminate a drift - a heavy character may retain enough speed to continue a drift even after contact with the wall. Contact with the "rough"/"grass" area of the track may also reduce your speed to the point where you cannot drift.
- A moment when contact with the ground is re-established - I'll call this the "landing point".
- Holding the jump button before the landing point and continuing to hold it through the duration of the drift. Releasing the jump button terminates the drift and activates any accumulated boost (blue or orange).
- Wheels are turned before and during the landing point. Turning your wheels during the jump (midair) is fine. After the landing point, you may continue to turn, go neutral, or counter turn without terminating the drift.
See also: a more nuanced description of bike drifting.