It's like setting points.
Look at the shaft and you'll see 2 lugs on it, turn engine over until one of the lugs is in line with the phase sensor pick-up. the gap should be between 0.2 - 0.3 mm. If you can use plastic feelers as the sensor uses magnetism and metal blades may effect it (I have used them though).
If this doesn't cure it check you've got the wiring plug the right way round, although they usually don't start the wrong way round.