Okay i have a 2004 400ex, with a slip on T-4 PC pipe, k&n air filter with outerwear air box lid off, 155 main jet, with the needle clip moved down one position, and mixture screw out 1/2 a turn. Also a 14 tooth front sprocket. Okay now that, that's said i just purchased a White Bros rev box and just wanted to know if anyone out there has one and if they can tell a diff with the WB compaired to the stock box, besides the higher rev limiter. I was told that the WB box advances the timing, if that true? When i put the new box on it seemed like there was a lil more power there, like it wanted to rev faster, but maybe its just me. So i just want to know if anyone else has one and if you can tell a diff between the two. Also has anyone had any problems with the boxes other then being hard to start in cold weather? Thanks ahead of time.

 

Yes I have (had) a White Brothers rev box on my 400 EX. I put it on last week. I noticed better take-off when the rev box was installed on my stock 1999 400 EX. By the way I blew the rings out in my engine due to the rev box... no I am not joking. My bike is at the shop right now getting fixed. Nearly $500 to get my bike back to stock. I suggest that you be careful with the rev box. They are mainly built for racing quads such as an EX with a 440 big bore kit, stage II cam, etc. I would have gone this route instead of putting my bike back to stock but it would cost nearly $1200-$1500 to do so. BE CAREFUL AND CHECK YOUR OIL BEFORE EVERY RIDE.

 

Thanks for the imfo man. I think i will just take the box off and go back to the stock one. By the way, how did your box cause you to have to replace your rings etc.?

 

I have a hard time buying this. I would think that a 5 year sport bike might need rings anyway. Or the fact that the rings seated to the cylinder and then were pushed past that point could be the case. Either way I don't think they are unsafe.

 

the rev box won't cause u to blow rings

 

Thanks again for the info guys. Also if anyone has this box, could you tell a diff in the power when compaired to the stock box? Also, thanks for the WB revbox TractorPacker, i got it today.

 

Come on now, i know someone out there has something to say about this.

 

ok, 1 person had a bad experience with the box, i dont think he blew his rings because of the box though. Plus he said he had no oil in it, dont take the box of and your 400 will be fine. Millions of people have WB boxes and their fine, their designed to work with a relitivly stock motor.

 

i consider those white brothers boxes next to junk. the main thing they do is raise the rev limiter. this can be really helpful on a built engine with an aggressive cam. otherwise, i wouldn't buy a rev box. i had a sparks box. same concept as the WB. they make the bike hard to start. a good rev box is the GT Thunder rev boxes. they make 2 different ones for the 400ex. one is more aggressive. this one will have a little irratic idle and the bike wont' want to stay started when cold. however, the throttle response on this box is much better than the stock box. it is a curve made for the 400ex. the sparks and WB are not actually made for a 400ex. i believe they are XR boxes. also, the WB box will make the bike near impossible to start in the cold winter. some say if you have a brand new battery, it can be started.