I have a 400 that is all stock except for rev. kit and a K&N filter it has the stock jets should i be able to richen it up enough by the fuel mixture screw or will i need to rejet. Where i live we are at sea level to 1000 ft. and what recommendations do you have on what to start with as far needle settings main jet pilot or slow jet any one have suggetions please let me know.

 

shook

Check out the tech section at this website:

HondaEX

Their tech section has an excellent article about jetting the 400ex. It is good reading and everything is easy to understand. Hope this helps.