Is this fixed track or spline?
Fixed track junctions can be a bit snotty and tricky to setup, however, the splines should work fine.
If this is a spline-created junction, ensure that:
1) The track is joined. The circles should be yellow and not white.
2) The switch lever is red and green, not just red.
3) The switch lever is placed in the circle or slightly forward
4) The track is smooth
A pic or pics would be helpful....
