Ok so my Father just bought a used 2005 Honda 400ex and it had all sorts of mods on it, Full exhaust system, jet kit, K&N air filter, rev box just to name a few. So I just recently bought a brand new Honda 2007 400ex and its completly stock yet when I raced my dad his seems to lack the get up and go like mine has at stock and his is completly modified, I believe the carb setting are all correct not sure what to do if anyone has any ideas for me post them up.

 

did the previous owner change any of the sprockets? that could be the culprit

 

sprockets could be a problem, but then again if the guy put a larger cam in without changing the original gears you can lose some low end grunt. but what was the outcome of the race. did your father pull you and win?

 

also, have you guys switched machines and tried a full race? It could be your riding skill is better than your dad's.....

 

i agree with the others we need little more info!

 

It just goes to show when you start doing mods you screw your machine up. If a guy wants a crotch rocket, he's always better off to just get the crotch rocket instead of trying to build one. I hope you get it figured out.