rev box?

[supernatural]

is a aftermarket rev box worth the money? if so any suggestions? would it make a difference on a 400ex that is piped and jetted compared to a stock 400?

no...save your money and buy something else...i had a wb in my 400ex years ago...i had trouble starting it one day...i killed the battery in it, and a brand new one i had just bought a month befire for my 300ex...this is what i was told when i asked about my starting problem...
"Lose the WB rev kit.

The CDI box comes from an XR250 kick start bike. It's equipped with a circuit
designed to help keep the engine from "kicking back" on the rider.

What it essentially does is not fire the spark plug if the engine doesn't crank
above a certain RPM. This preset RPM level is just barely under the normal
crank speed of a 400EX... So, throw in some thick oil & cold temps, or simply
a low battery, and it's just enough to cause the engine not to start.

To verify that this is your problem you can do two things. You can put the
stock CDI box back on and see if it fires right up (it probably will), or you
can roll start it.

When I had this CDI box on mine, it was obvious. My quad normally fires off
extremely easily, but after installing the box, it wouldn't fire off when cold &
first start of the day - wouldn't even hit. If I went out and roll started it,
it would pop off cleanly like nothing was wrong.

After doing that a couple times over the course of a few days, the next time it
wouldn't start, I simply switched CDI boxes (back to the stock unit). After
cranking for what seemed like forever with the XR unit (without even a hit), the
stock CDI popped off instantly.

What it all boils down to is unless you have a highly modified engine with a
wild cam and high compression, the CDI box is not doing anything but taking a
safety net away from your engine & causing it to be difficult to start.

If you have the mods to support it, there are a few engine builders out there
that have figured out how to eliminate the rev-limiter out of the stock CDI,
which avoids using the XR250 CDI and it's anti-kickback circuit."