[Mcar raptor700]

I have a 2006 Yfz 450 and when I start it, it runs perfectly but once I rev it most of the time it stays reved high and sometimes dies down. It was running good about a year ago and slowly started doing that.

What do you guys think it could be?
Carb is all stock
has slip on Yoshi that’s it

 

[Yfsheee]

sounds like an air boot leak or clogged main/pilot jet