I'm new at this KLX250S experiment.
Lovin' the bike so far..400 miles so far and SO fun!..but..
...just hit my hardest off-road hole, while I was goosing it pretty hard, all the weight went to the back tire big time,, as I hit the hole like that I heard this alarming, definite 'crack' sound..like metal cracking somewhere it should not.
I've done a close visual inspection and see nothing obvious..anyone have
any guesses, from experience, what that 'crack' might have been? Thanks!

 

Maybe check shock linkage? (i.e., mounting points on both ends.) Seat area subframe? Swingarm pivot?
Just guessing. I don't have experience with the KLX.

 

I'm sure it was the chain slapping onto the plastic chain guide.

 

yeah, my chain "guard" used to get slammed by the chain took it off and bairly hear the chain now

 

x2 .

 

I think you are right..looking closely I see the upper chain guard,,that small round one bolted onto the frame above the chain, looks like it got 'activated' ie slammed pretty hard when I came down on it like that..but no harm seems done, just sounded awful. Great, uber-fun bike so far!