Best 400ex mods
 

I have the basics. Sparks full exhaust, K&N filter with prefilter, air box lid ON (I ride a lot of water, Doesnt bother me with the little less power) Jets, Swing arm skid, 450r front shocks, aftermarket ECU, and new plastics. After all these things, without tearing apart the motor, is the best mods for this bike. I am talking full out. :lmao:

It may also have a cam, not sure.

Also, what would be the best gas Octane rating to run in the bike?

I run either mid or high grade in mine. I also have the K&N air filter with lid. As far as a good mod. I would say a stage 3 hot cam. You seem to have everything else. What are you trying to ride. GNCC, hare scramble, MX?

GNCC. I ride just about every where.