i got a 2007 honda 400ex about a month ago, i was going to buy the z400 but the honda was $800 cheaper because it was a leftover. i'm wondering what is the best setup for me. i ride through trails and through open fields. i'm looking to get as much power as possible without risking reliability. it's completely stock right now. thanks

 

Sounds like you need all-around improvements, that is, both low end and high end. These will perk the engine up quite a bit.

The usual mods without tearing into the engine are: Remove airbox lid (I highly recommend the EHS Racing lid, with Outerwears), get a better flowing air filter (highly recommend ProDesign/ProFlow unit with foam filter), and an aftermarket header and muffler (I like FMF PowerBomb header and quiet Q4 muffler).

After that, you can do gearing changes to fine tune for your patricular conditions.

 

what he said.
But you can also maintain pretty much the same reliability if you do a 11:1 piston and an xr400r camshaft. I haven't had any reliability problems with the hotcams cam in mine but since it's not a honda part I am sure someone will disagree that it's just as reliable. I would say the higher compression makes the biggest difference though, and allows you to run a slightly higher gearing without as much bottom end loss.

 

thanks for the help