THE 1% RULE.
Try this it works.Employ the 1% rule.At 1% of your current ground speed, distance from your LNAV track (cross track error or distance from) select a heading towards your next LNAV track and then press the LNAV button.Works regardless of speed.For example if you try to use LNAV to join a DME arc at too high a speed 320 knots etc, it often will overshoot the arc, but if you commence your turn at 1% GS in NM you will roll out on the arc.....Peter