I love jumping, and made an interesting discovery which I overlooked at first: maybe it is the jump itself? Here's what I discovered last week, though probably elementary to seasoned riders...
Was having a tough time with nose-downs, on about half of the attempts I was making while in 3rd gear. (All the 2nd gear jumps went fine). I thought my body position or throttle habbits were at fault until I had a friend video tape some footage of the particular jump I was having trouble with. Now throughout the taping I tried varying body position and speed, wanting to be able to see what the differences were in playback. Hitting in 2nd gear was fine, but about all the jumps in 3rd gear produced results less than "safe".
We watched the tape in half-speed playback right on the camcorder, and noticed right away that the suspension was completely squashing out when entering the face of the jump. This was a relatively short jump, and the only one which wasn't flooded out from recent rains, or we would have gone elsewhere. But the
major problem was that this jump had (in some spots) a harsh angle between the take-off and jump face... something I didn't figure would matter much - hey that what shocks are for, right? Well kind of.
example of what this jump face was like: If you hold your left hand flat out in front of you, and force your fingers upward sharply with the palm of your right hand, that's how certain spots of this jump face were. Almost a direct, hard 45-degree angle -- just too drastic of a transition for fast speeds, instead of a smoother arc.
With the forks and rear suspension bottoming out so quickly, the jolt continued through to my body position, affecting the important take-off stance. In playback, we noticed when I hit the jump fast, the suspension would bottom instantly and my upper body continued forward
just enough to mess up a good in-air stance.
A little more compression damping has helped, but I learned not to hit jumps so hard when the take-off transition isn't sloped smoothly. It's like asking for a rough landing. Not that it isn't fun trying to learn how to overcome the bike wanting to nose-down during sharp jumps... but moving to a smoother jump has made it possible to hit this one faster, making the in-air time more enjoyable and the landing MUCH less "OH NO-ish!"
Hope this helps.
Also, maybe try a different jump if you can. And make sure the top of the jump is smooth as well (sometimes they get a lip worn into them). All of this I've noticed can affect how you end up coming down.
good luck,
matt