Im trying to learn some speedy legato licks to slot into solos and riffs I write. I've been using triplet legato, plucking the string on the bat, then pulling or hammering two notes. Ive been using 6 notes per beat too.

The problem Im having is playing 16th note legato as it involves either moving my fretting hand up or down the next to change position or moving strings to hit the fourth note of the four note per beat. Im so used to plucking the string on the beat and playing two notes after it that im having trouble adapting. I can play 16th notes in time when I just use alternating picking, and I can play 16th note with legato if I stay on one string, but the problem is when I have to change string in the middle of the 4 of the 16th notes.

Any advice?
It's really just a case of slowing things down and practicing.

Take any 16th note lick you like and play it slowly to a metronome, really focusing on the timing of each note. Try and break the link in your head between the first beat of the bar and the picking of a string.

You almost have to forget that you're using legato technique and instead just play the notes.

This is almost certainly a 'mental' issue, not a technical one. If you can play 16th notes with picking, and 16th notes with legato on one string, then it's just a case of reprogramming your thinking.

Try and break it down into 4 note phrases. Play the 3 notes on one string followed by the 4th note on the next string then stop. Get used to picking (or hammering-on from nothing) on the fourth beat of the bar.

Actually, hammering-on from nowhere may be a good thing to try here. It will remove the picking hand from the equation all together, and may help you overcome your rhythmic problem.
One thing I've found useful is taking a legato lick, and playing it a few times picking every note. Once the timing is solid with the picked version, play it legato and mimic your timing from when you were picking everything.
Thanks for the tips chris and se02101. I'll give those tips a go.