What exactly is the BK mod and why do it??

9 replies to this topic
  • Weezer_#_1

Posted February 14, 2002 - 06:53 PM


I just got my '01 426 about 2 weeks ago and am researching like crazy.
One thing I have noticed is this BK mod.
What the hell is it and why do it??
Thanks all!!!

  • 668MXer

Posted February 14, 2002 - 08:11 PM


Do a search on it. Motoman393's website has great intructions to do it.

  • skthom2320

Posted February 15, 2002 - 05:03 AM


Ride your bike first. Decide if there is in fact a "bog" down low that you just can't live with or that cannot be removed with proper fuel screw adjustment, pilot jet, etc.

I have NOT done the BK mod. I have plenty of snap down low. A fellow TTer who had done the mod on his 2001 rode my bike recently. He ended up rejetting and removing the BK screw on his bike which resulted in as good or better performance than with the BK mod.

Others have reported no improvement as well, mostly on 2001-2002 bikes.

It seems as if improvements in stock jetting and ignition maps from Yamaha are eliminating the need for the mod on the '01 and newer bikes.

Anyway, you can do the mod and see for yourself if it helps. It is easy enough tu "undo" it.


Steve T

  • Weezer_#_1

Posted February 15, 2002 - 08:16 AM


Thanks...I have a 2001. Haven't noticed anything so far but I'll keep an eye out for it now.

  • motoman393

Posted February 15, 2002 - 09:41 AM


I didnt have the bog either before the BK mod, but for $5 it is worth a try! My bike runs much better and 5th gear wheelies are easy LOL! I richened up the needle and main (left the pilot at 42) Later,


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  • Weezer_#_1

Posted February 15, 2002 - 11:12 AM


What is your needle position and what main jet???
Do you have a pipe??

  • Taffy

Posted February 15, 2002 - 02:45 PM



mine wheelies in sixth :) :D

Taffy :D :D

  • motoman393

Posted February 15, 2002 - 03:36 PM


Do WR's have 6 gears...or is this an "a la Taffy" mod? Mine would wheelie in 6th gear if it had a 6th gear LOL! Later,


  • b-bike

Posted February 15, 2002 - 05:19 PM


Yo Weezer:

I just came in form the garage where I finished doing the BK mod to my 01-426. (Yes, my bike had a bog on the bottom end.) :) I used the information form the web sight that 668MXer told you to check into. It was one of the easiest mods that I've ever done. I can't wait until I can throw a leg over my "Blue Beast" again and BLIP the throttle to check out the responce form the bottom. :D :D

  • therapture

Posted February 15, 2002 - 07:14 PM


Originally posted by motoman393:
I didnt have the bog either before the BK mod, but for $5 it is worth a try! My bike runs much better and 5th gear wheelies are easy LOL! I richened up the needle and main (left the pilot at 42) Later,


I did the mod as well, easy to do, but having a hard time curing ALL the bog...it seems snappier on the stand, but riding tomorrow will be the ultimate test. I had to richen the pilot to a #48 which is way fatter than the stock #42, but stock jetting was WORSE after the mod, I have a 168 main in at present, and I think I will be ok there, but I have *almost* all of the bog out after adjusting the pilot screw. Would richening the needle help any?

Still has enough bog off of idle to make life irritating...if it pulls better I might not worry about it, but unless there is a noticeable on track gain, I will remove the BK mod in a hurry....

Any ideas? BTW, I am in same area as motoman393 (south texas).

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