Bk mod pic's

Here are some pics of the BK mod.

There were a few people asking about pic's of the mod so I took some when I had my carb off.

I used a 6-32 x 1" long machine screw with a number 36 tap drill.

I needed a spring but couldnt find one long enough so I used 2 that I found on an old weed eater and just put a washer in between the springs.

Pic's didnt post...........Damn

oh well I tried.............


[This message has been edited by jaybird67k (edited 07-31-2001).]

[This message has been edited by jaybird67k (edited 07-31-2001).]

[This message has been edited by jaybird67k (edited 07-31-2001).]

[This message has been edited by jaybird67k (edited 07-31-2001).]

[This message has been edited by jaybird67k (edited 07-31-2001).]

It looks like Jason was having a hard time posting pics...so he emailed me them. If you want to see them click HERE I will update the page whenever I get the chance, I just wanted to post the pics since many people have asked for them! Thanks Jason for the pics and info!



I get my kicks on a 426!

Motoman393's MX Site

Great pics - probably the best I have ever seen in terms of showing detail!!!!!

The mods are what I envisioned - however, I do remember adjusting the upper screw when I first got my bike - don't forget I am the one who's bike WAS THE WORST for the cut-out.

Anyway, who can explain why the BK mod is as good as claimed? Is that because it acts as a positive dead-stop on the rod travel? Must be so.

Did you try Lowe's hardware for the long spring?

Thanks again for the pics guys - I have been waiting and waiting for those.


Excellent pics! Thanks Garrett and Jason.


00 YZ426F

01 TT-R125L (my son's)

74 Hodaka Super Combat(gone but not forgotten!)

Thanks for the great pics!! It looks vey simple now that I have seen the pictures.What kind of improvement did you notice in the powerband? I'm sure it ended the bog problem!

Thanks again!!

Great pics. Why didn’t you just cut the screw?


The whole point of this mod is to shorten the pump stroke. This shortens the duration and amount of accelerator pump discharge whenever you twist the throttle.

Total stroke on a stock carb is limited by the button on the pump diaphragm which eventually bottoms on the inside of its housing after the rod travels about 3 mm. Using the mod pictured I have cut this to 1 mm, after considerable experimentation I always end up at roughly the same adjustment.

An additional benefit is the pump is easily disabled with the screw, and jetting your bike with the pump turned off is the best (and easiest) way to do it. Then turn the screw out until you get the best throttle response.

This has all been covered before.

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