There are so many factors that could affect it - I'd highly recommend any of the Peter Hart how-to videos.
How much you lean into it depends on how windy it is. If you're on a big board in light winds, then leaning in too much will stall the board on the big rails, but on a wave board in high winds...
It's easy to pick how others are doing it wrong, but hard to see it in yourself - I'd reckon most folk leave the sail change way to late (need to flip the sail as you head downwind, not when you've "come around"). Some bear off for far too long without turning and then lose all their carve speed, some don't tighten the carve on exit...others don't lean forward enough and end up sinking the back of the board.. I know I'm guilty of all of the above.
If you can get the wife/girlfriend/mate down there with a video, you'll pick your problem in seconds...
Have fun ... Lozza
