I learned an improtant lesson about White Brothers spark box and also the 250 box swap. On a trip to a very cold environment my 400 cranked over but would not fire (no spark) and ran the battery down. The worst part was being pull started by a damn Banshee! When I got back I went to the dealer and called my motor builder to get two educated answers to what had occured. Here is what they told me: It turns out cold start problems are common with spark box swaps. The CDI box looks for a minimum RPM before it allows spark (to prevent kickback). The min. spark RPM for electric starter engine CDI's set lower at 70 RPM so it will fire in cold weather where battery voltage is low and oils are thick. In warm weather the EX turns over at 105-110 RPM so in those conditions other boxes will work most of the time. The 250R and WB box are derived from manual kickstart motors that spin over much faster than electric starters and have a min RPM of 100 to prevent kickback and injury. I plugged my stock unit back in and it starts much easier. TC Racing makes a CDI with the lower min fire program. Also the only real benefit is 1000 more RPM the spark advance in negligable the stock box max advances before 3000 RPM. I have a cam, piston, carb etc. and mine doesn't make useful power over 7500 RPM so anything over the stock 9200 rev limit would loose the race anyway. Sorry so long but I felt I would share a lesson learned...

2000 400EX
AC Pro Peg nerfs
Graydon full skids
Renthal stock bend
Pro Kill sw.
Magellan 315 GPS
TC Racing 425 motor w/ track cam, 10.5 piston.
Ported head, tricked carb.

 

thanks for the info.i'll check mine out,i'm having
the same problem.my jetting is spot on.i was going
to change the heat range on my plug,but,i think i
will check that first......
ct 440 kit
web cam & hard faced rockers
k&n filter
quiksilver carb
big gun system

 

This doesn't make sense to me.
An electric starter spins an engine 110% faster than anybody could ever kick-start any bike.
I'm sure your right about the spark program, it sounds a little backwards though.

 

The overall duration of electric is longer (as long as you hold the button) but the instatanious rpm of kickstart is greater but doesn't last as long. I didn't guess at this both the motor builder which has been building top 10 GNCC motors for years and the Honda dealer asked me the same question when I complained about cold starting (did you change the CDI?) they see it a lot. They gave me the same explanation of why so I plugged the stock one back in and easy as pie ever since. The WB CDI did start in most conditions just not on that one cold trip. It always required more cranking than the stock CDI though. But why use it? Even cammed built motors don't pull over 8 grand especially big bores, 9200 is plenty.

 

Having the same problem with mine and all my friends. We just carry a stock box or push start when it's real cold. Once it's warm it's fine.

 

my buddy has same problem with his 99 400ex.No matter what the temp, if its been sitting it wont start with WB cdi.Swaps in orig box warms it up then switches back to WB cdi box.jetting is perfect.He got WB unit traded in for another one and still same prob. Now my 00 400ex never has a problem with its WB box.Fires right up always on first or second hit no matter what.