Okay.

[factoryX]

I'm having an issue with lurching forward(body shifting forward) on my 03 yz250 when ever I use it for trail riding, and I didn't used to do this on the KDX. I've only been riding bikes for a year now, and I feel that I'm kicking ass and taking names but this is getting kind of annoying especially when you're in the middle of a rocky trail. Any advice would be great.

[tirebiter]

Try higher bars, heavier flywheel and lower overall gear ratio.
Powerwise, 2 stroke MX bikes tend to 'sign off' earlier when the RPMS drop than more mildly tuned trail bikes, creating a power 'Void' so to speak. On the way down, their either off or on with very little usable gray area in between.
that sudden abrupt loss of power causes a whole shitload of changes- to the geometry of the bike, and how a rider responds.

[factoryX]

Okay I get it, when I let off it practically shuts off, so in a way its engine braking(Weird). Power delivery on this bike is near perfect, climbs everything and rides trails great. I'm already planning on a 52t sprocket to have a better power delivery(14/50 currently). I'm running Pro Taper Contour bars with a half inch riser fat bar adapter, so there's no problem there. Other than that one set back I don't regret getting this bike.

[gsa102]

Try to practice changing your body position to account for the cut-off. Body forward under acceleration, body back under braking and deceleration. The big 4ts will wear your arms out if you don't.

[factoryX]

4t?

The bike before I did some work to it.

[Julien D]

Yep, when you can think about it, practice moving your body forward when you're on the throttle and then back when you left off or brake. The more you conciously do this when riding the more it will become a habit and something you don't even think about.

[gsa102]

Just comparing it to my 450F which has massive engine braking...

Conventional wisdom says to grip with your knees, but I can't quite figure that out. But at 6'1", I am a little taller than what they consider to be the average rider.

[kawagumby]

On 2 stokes or 4 strokes I always disengage the clutch when decellerating regardless of speed. That allows me to keep the revs right where I want them, and I can use the clutch to act like a lower gear too while actually being in a higher gear. You get less rear wheel bounce too as you have more control modulating the rear brake than using engine braking (even with a 2strk). When in really tight stuff the hand is always on the clutch - and varying the engagement is key for smooth riding. On more wide-open trails you can come into a turn a gear high that way and really boogie out.
I will use 4strk compression braking in some situations, but not in tight stuff.
Using that method will eliminate stalls and down hill rear-end swaps too. After a while it will become second-nature.