I have a 400EX that I am giving consideration to purchasing a 250X CDI to get more RPMs and bypass the rev limiter on my bike.

The bike in its current condition is stock, and I plan on adding a WB R5 pipe to it, but I have heard some problems may occur with these new rev boxes.

Has anyone experience motor failure or an engine that needed to be rebuilt because of a new rev box?

Blake

 

Well, the box you are looking for is probably the XR250 unit, not the 250X unit (unless they are the same, not sure myself).

I bought the XR250 unit, haven't installed it yet because I haven't put my engine back together yet. I made camshaft, compression, and head porting adjustments though. i wouldn't recommend changing the rev limiter for a stock bike. The engine's powerband is falling off rather quickly by 9,200 rpm and anything beyond that is really not necessary.

 

actually ive seen those rev kits bring 400s and 300s alive...ive heard really good things out of tc's and sparks.......only complaints ive heard out of them are from white brothers....however, ive seen allot of tt racers and mx racers only install these boxes but said to put heavy duty springs in when installing, and they said they could tell a pretty good difference......i plan on getting a 3 angle valve job (head work) and springs with the tc rev kit with in the next week or so.....cant wait!

 

I wouldn't recommend putting one on a stock 400ex either. It will do you no good, until you start to mod. it. Do you hit the rev-limiter right now? I had a W.B. cdi on mine and every time i left my 400ex sit overnight, it wouldn't start the next day. I had to keep swicthing the stock cdi and the W.B. cdi to get it to start, so i just put the stock cdi in and just left it in. I no other people have had the same problem with the W.B. cdi. I am constantly hitting the rev-limiter now though, with the stock cdi. I will either get the TC or Sparks rev box.

 

I installed a WB unit and have not had any problems. I would say my 400ex is hard to start and is cold blooded until well warmed up, but it was that way with the stock CDI.

 

Jaxberg, mine wasn't cold-blooded. The W.B. cdi wasn't giving the engine spark. I would put the stock cdi box back in, and it would start right up. pretty weird huh?

 

1QuickEx, very weird indeed. I actually have been very pleased with the WB unit. I also know many who haven't. Luck of the draw? I've raced many mx races since installing it and did a lot of trail riding as well with no problems. Time will tell I guess. I see there talking about snow in northern MN. Time to get the sleds ready huh?

 

yup jaxberg, I can't wait for snow. Atving is fun, but there is nothing better than 130 horsepower underneath you heh?