Idiot's Guide to More Power on 400ex

[fwhite02]

Gradually trying to increase power on my son's 2002 400ex. We hav installed WB exhaust and are using the WB filter provided. No re-jetting yet. I am looking for recommendations for next couple mods. Riding is mostly very sandy trails. Thanks for your help.

[400exdad]

1. If you're running the stock headpipe, grind the welds on the inside of the flange where it bolts on at the head. Look for some posts if you want to see some pics. When you get the headpipe off, you'll see what I mean and know what needs to be done. Just don't grind all of the weld bead out. The gain for me was that it would RPM more easily and I could feel a good pull in the midrange.

2. Go up on your pilot jet to a 42. The main thing this will do is make it start easier. Check my signature for my mods. With the 42, it will not be too rich.

Good Luck and welcome to the Best Forum on Earth. :D

[OCCRA288]

After you get done grinding the welds, Look at geting a Higher compression piston and cam.

JE makes a 10.5:1 piston that works really nice in the stock bore cylinder. And for a cam I got the Stage 2 Hotcam, I felt great increases all the way through. Bottom pulls hard, Mid range has a nice kick to it, and I still haven't topped it out yet.

Installation was easy. Get a Honda Service manual and you'll have all the instructions to disassembly and reassembly.