Loss of power down low

So I have a 09 WR250 X and it is great fun I usually act a fool on it and pop the occasional wheelie. Well recently the bike has no balls down low, when i try to clutch it up it might get an inch or so off the ground, if i REALLY try I can get the front end up but it takes WAY more effort than normal. the bike feels less quick off the line as well. It doesn't feel like a roasted clutch it's more just a lack of power. I havn't changed or added anything to the bike it just started doing this randomly PLEASE HELP!

Specs on the bike:
4000 miles
full FMF
K&N
Flapper glued open

Air filter need a cleaning?

I took the filter out checked it, it was pretty clean all things considered. I looked over the exhaust, it looks normal, I will pull the plug and check it but I'm running out of ideas.