should i run with out the air box lid on my 2001 400ex with k&n air filter hmf slip on and jet kit??

and would it be a good idea to put a 450r carb on my 400ex?? will it give more power?

 

I would remove the air box lid if you have a new filter pipe and jet kit, you probably won't feel the difference, but its there. As far as the carb goes, assuming the 450R is larger, then it will most dump more fuel, which can in turn lead to increased power if the bike is able to burn it all.

 

EHS Racing airbox lid. Filters out the big stuff, with very little restriction on air flow.