O.K., I know this is an old subject, BUT, I read on another forum that the XR 250 CDI box and the White Bros are the same, O.K. cool. I also read that both of the CDI advance the timing by 5 or 6 degrees (that is why it is little harder to start when cold).

Is this true? The reason I am asking, I was going to buy a timing advance key (+6 degrees) and a CDI Box. But if the box already advances the timing I would be at 20 degrees BTDC...that sounds way too much.

I want this mod for a couple of reasons, I want that motor to rev out a little more, but I don't want an unlimited RPM. Also my motor feels like it is still pulling good when it hits the rev limiter. Also I am hitting the rev limiter in 5th at the races in several spots.

Maybe I should put a 15 T back on the front, since first gear is nearly never used and the motor can pull a larger sprocket.

Thanks for the help.
Nick

426EX GNCC

 

No, it wont advance your timing. The reason it is harder to start is becasue the motor needs to turn at a faster rpm to start, so in the cold weather the starter cant turn it over fast enugh. The confusion might come from the xr400 having +6 degrees timing.

 

I also have a hard time believing that the WB box advances timing like advertised (also note that it doesn't just move the Rev limit up 1000 RPM like advertised, as that machine is obviously turning 2000 RPM above the stock limit). Take a look at the dyno run on GT Thunder's website, the HP curve for a stock CDI and a WB CDI are the same. If the timing were altered you'd see it on the dyno chart.

http://www.geocities.com/gtthunder.geo/400cdi.jpg
Copy and paste the link into a fresh browser window, geocities wil block it otherwise.

Also, yes, I highly suggest going back to a 15T front sprocket. In fact I am going to a 15/36 setup for XC racing on my quad. My machine felt stronger on a 15T front than a 14. The 14 was just too low and the gears were too tight. I shift much less now, and it feels like my powerband is wider.

Gabe

 

Thanks for the reply guys, I ordered an advancer this morning and will have it on for the Ironman this weekend. I don't have CDI yet, but I will soon. I believe I will go with an XR250 box, but only after I confirm that it will raise the rev limiter 1000 rpm.

Gabe; It's been a while since I have seen as post from you, glad to see your back.

I read on EX riders that someone said that it did and I can't see how, since the trigger for spark is from the flywheel.

Nick