is the bk mod for me???

6 replies to this topic
  • screamin426

Posted October 03, 2001 - 03:26 AM


hi all,

i have a 2001 426 that has no blubbering problem at all, the throttle response is superb,will the bk mod make it better? i'm always looking for more power,will this help in that dept.? i'm running a fmf power bomb header and power core iv-2 s/a,my jetting is 175 main,45 pilot,stock needle and position,1 3/4 turns onthe air/fuel screw, phillips 76 110 race fuel.



[This message has been edited by screamin426 (edited October 03, 2001).]

  • Ga426owner

Posted October 03, 2001 - 05:56 AM


I believe that if your bike does not have the bog, from opening the throttle up, then the mod will not be noticed. Some others may disagree, but like yourself, my 2001 bike does not bog, even when I whack the throttle open as fast as possible. My 1999 & 2000 426 had the bog & it drove me crazy.

  • Ramrod

Posted October 03, 2001 - 06:30 AM


By doing this mod and shortening the gas spray duration (ie. 4 secs to .3 secs) - will this be better even if you don't notice any differences because you won't waste as much gas when you stab the throttle?

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • sirthumpalot

Posted October 03, 2001 - 07:40 AM


I've got the '01 myself and I don't see any need for the mod either. I've never experienced any bog or blubber and the thing pulls like crazy from bottom to top. It got the ultimate test during my last ride in the whoops where I went from fully shut to fully open very quickly many times while attempting to keep myself on two wheels and it never missed a beat. Some people say they see a difference but I have to wonder if it's due in part to the fact that they're also taking time to play with the jetting at the same time that they do the mod. As I understand it's necessary to rejet after the mod but I'm wondering what the difference would have been with the rejet only. It's possible that I don't know what I'm missing, but personally I'm very happy with the way that it runs for me and I'm not going to fiddle with it. :)

As far as wasting less gas, I am going to guess that it's not enough gas to make a noticable difference as far as fuel economy goes. I'll guess that the larger main jet that some people are using may even swing the gas usage in the other direction on tracks where the throttle is open often.

  • Hick

Posted October 03, 2001 - 08:56 AM


The ’00 has a MUCH worse problem with throttle response relative to the ’01, and I agree that a lot of the experiences with this trick may also be jetting related. On my ’00 and ’01 I had already addressed the jetting issue before I did the mod. At any rate I saw no need to change the main or clip position on either bike afterwards. BTW, long before BK showed up, on a tip from a road bike guy, I disconnected the pump on my ’00 in order to jet it. Being a thumper neophyte at the time this made things obvious to me and (with the help of a few TTalkers) I ended up with basically the same jetting as the stock ’01, long before it was released.

So the difference I noted on the ’00 was from the BK thing was identical to that I noted on the ’01 since both had (almost) identical jetting at the time I did the mod. Being at altitude may make this more beneficial for me, but I also think that once you become accustomed to the stock throttle response you may be “riding around” the problem, having become accustomed to the point of not noticing it. If you don’t notice it on a stock ’00 however then you are in some kind of denial :)

It is not a huge difference in every situation, but I suppose a descriptive and universally applicable anecdote would be that little first gear wheelies at low rpms are a much easier and smoother exercise with the shorter pump stroke. I need a bit more throttle control and body english with the stock pump setting. This was reinforced as I rode my new ’01 for a bit without the mod while waiting on some parts. BTW I needed a bit more delay (like a half turn) over stock on both bikes for things to work well.

I’m not a big (or very accomplished) wheelie practitioner, but I can honestly do more consistent and longer wheelies through the gears with the mod. It doesn’t help only your wheelie prowess, I’m just trying to use an example we can all relate to (and who doesn’t do the occasional wheelie to impress the neighbors?).

Don’t forget you can do this and always run with the screw turned out to go back to stock.

  • motoman393

Posted October 03, 2001 - 04:02 PM



I thought the same thing you did before the BK mod..."my bike already is crazy fast and has not bog why should I mess with it"! But I thought what the heck it costs $5 and if I dont like it I can simply remove it. Well after doing the BK mod my bike is no longer crazy is Mach 1 LOL! There is a huge difference mainly is acceleration and it rips all the way through the powerband.

I had to change my main jet to a 168 and richen my pilot up 1/2 turn to compensate for the lack of gas being sprayed from the pump. I am very satisfied with the results. Just dont tell your riding buddies about it, and then let em' ride your bike one day! Watch the grin on their face when they come back to the truck! LOL Later,


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

  • Guest_Guest_*

Posted October 04, 2001 - 03:27 AM


I am amazed at the variations I have read about on the pump shot duration. Mine was just short of 2 sec. before mod. I have heard some guys say theirs was 4 sec. How can they come set so differently?

Related Content


BIGBORE FOR YZ450F 2006? by Taattie94

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • 5 replies

Chubby dad, looking at bikes , First trip to the orange/black forum ! by Slow_ride

Dirt Bike   Make / Model Specific   KTM   250-530 EXC/MXC/SXC/XC-W/XCR-W (4-Strokes)
  • Hot  28 replies

Wilson the Blue Privateer by jetfuel

Dirt Bike   Special Interest Forums   Pro Racing
  • Hot  50 replies

Yamaha YZ450F 2017 by Chris.GVS

Yamaha YZ450F 2017
  • * * * * *
  • 1 review
  • Last review by Tommyk_55
  • On January 15, 2017

Is it worth it? (Cam and High compression piston) by macgi77

Dirt Bike   Make / Model Specific   Honda   CRF 150/230 F/L
  • Hot  36 replies

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.