I bought my 400 EX new last fall. Had a White Bros. pipe put on at the dealer. I've left the engine stock other than a K & N filter and tweeking the airbox lid for additional airflow. I've been procrastinating about changing the jetting until today. The stock jet was a 148, I changed it to a 160. Additionally, I ground the welds flat inside the headpipe. I put everything back together and took it out...WOW! It easily wheelies in 3 gears. This is awesome. I recommend it to all 400 EX owners.

What are the best mods that you've made to your 400 EX? Were they expensive or inexpensive?

Thanks!

Brad

 

I stroked the crank 4mm and bored it over 2mm. Yes it was expensive but it will loop out in fifth with stock gearing and 22 inch razr2's. It has more torque than my 450r.

 

i vouch for that

and it seems real reliable too

 

92mm piston + 4mm stroke