float heighth?

i have a small problem with my bike. I have a 98 Ktm 125 exc and i run it exclusivly in the woods. I decided to let a friend borrow the bike for a motocross the is coming up. He began to practise with the bike on a small jump at a hare scamble track we have, and every time he landed the bike would bog terribly. RPM's would drop form almost redline to just above idle. What is the proper way to check the float heighth on the Keine(spelling?) carb that is on this bike. Could it be something else? Also,I have ordered a V-vorce reed block for this bike, what type of changes should i expect to make to the jetting/pipe. Will the stock pipe/FMF silencer work ok? thanks in advance for any advice.