What is a BK mod.

3 replies to this topic
  • candlkirk

Posted October 18, 2001 - 03:02 PM


I just bought a 426 yesterday, and I hear everyone talking about a BK mod. What is it and what does it do? Also how much do all of you use your clutch and how important is it to use your engine braking on the 426. Can you ride it without using it?

  • motoman393

Posted October 18, 2001 - 04:09 PM



First of all the BK is a "factory secret" if you will that Brian Kinney (Tim Ferrys mechanic) told us about! This modification limits the accel. pump spray duration. From stock 1.7 secs to .3 secs it gives your bike ALOT more snap (like a 2 stroke 250) and makes it start easier. You can do a search on the "BK mod" and you will find TONS of info about it...because I am sure people are tired of talking about it. If you want some pics and a procedure on how to do the "BK mod" I have them listed on my website: http://mx393.tripod.com/carb.html I would wait until you get used to your bike because this mod really gives the bike alot more snap...in a few months you will want more power (or at least I did) LOL!

About using the clutch...many people on here dont use the clutch at all (except for taking off) but after hearing about trannys exploding I am not going to risk it. I always use my clutch when shifting. The 426 is different in corners that 2 strokes, it likes to be lugged. I never pull the clutch in on turns (unless I am about to stall). The 426 is almost like an automatic I just put it in 3rd and either chug or rev (make sure you turn your idle up a tad, so it wont stall as easily)

Engine braking is your friend you will learn to love it! Welcome to TTalk...you will learn ALOT here, I know I have! Later,


I get my kicks on a 426!
Motoman393's MX Site

[This message has been edited by motoman393 (edited October 18, 2001).]

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  • john.hilton@cape.k12.de.u

Posted October 19, 2001 - 01:44 AM



I went to your site to finally see what this BK mod is all about. This doesn't seem to complicated. However, I have a couple of questions.

1: Does the entire modification consist of drilling and tapping the hole for the screw, installing the screw,then adjusting the timing and spray and possibly the jetting?

2: If you do this mod, and don't like the results, or can't dial in the jetting, can you simply remove the screw and readjust the spray timing back to stock settings?

3: I have an 01' YZ 426, and I havn't noticed a real problem with a bog right off idle. Will this mod really make a difference that I'll appriciate? Assuming I get the jetting right.

4: On your pictures, I can't figure out what the screw you installed does. The black cam seems to only be able to rotate counter- clockwise, and the screw you installed isn't touching the cam. Do you have the screw threaded out for the pictures, or is there something that I'm missing?

Thanks for your time !!!!


  • motoman393

Posted October 19, 2001 - 11:07 AM


I dont mean to sound like and @$$ but all the info that you are looking for can be found if you use the search button! Here is the link to the search: http://www.thumperta...intro&default=6 Search for "BK mod" or "BK" and select "all topics" and you will find at least 100+ entries about this mod...and you dont know how many times I have explained how to do it! Hope this helps,


I get my kicks on a 426!
Motoman393's MX Site

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