I ride a 00' 400ex w/White Bros. Pro-Meg System, K&N Power Kit with 170 main jet, AC bumper and nerfs, I also have modified airbox w/6 holes. What should be my next step in getting some more power out of it? (preferably without sending anything off) I was thinking about a rev box or should i wait until I get some more mods to get the most out of it? Any help would be greatly appreciated.

 

I have about the same setup as yours. I had a 170 main jet in my ride. I tried this: I let the quad set while idling in neutral. I held the throttle wide open and it appeared to be hitting the rev limiter. Now I put a 165 main jet in and hit the throttle again. The difference was very noticable. The RPM's were higher. Apparently, for my ride, there was too much incoming fuel for higher RPM's. The Spark Plug looks better and the quad does perform better also. Note: Before changing the main jet, my plug was pretty much black. I know that it should be light brown, but all I was thinking at the time was - the more fuel I can get through the machine without fouling plugs, the better it will run. Wrong!

 

Your standard rev limiter is set at about 9000 rpm,the 400 ex makes peak power at about 7000 rpm after this the horsepower drops away, so if you increase your rev limit to 11,000 rpm your pretty much flogging a dead horse, and giving your motor an unecessary work out.

 

Hey buddy,
I know of five guys I ride with,including myself, that have the high rev CDI box. If you know of anyone that has one,ask to borrow it. You'll find the ignition curve will make the engine rev quicker!! My brother-in-law,last weekend,was riding at Little Sahra State Park in Oklahoma and with the same set up you have,brought his 400 up in 5th gear!!! Scared the hell out of him,he had to hit the rear brake because he was going so fast that the air caught under the front end and almost flipped him over!!!
.....Dave/'99 400ex

 

Thanks for the info fellas but what should I add other than the rev-box?