Bog after bk mod

I have recently done the bk mod and have developed a bog off the bottom. I can back out the screw back to stock and the bog goes away.

My setting are 38pj, 60 paj, emm-3, 155 mj, 160 maj, yz timing, wb e-series pipe with 9 disk.

I did not have a stop watch to time the duration but have just a short squirt. Stock duration was about 4-5 seconds.

Any ideas? I don't think I am too rich because I just changed the needle from clip 2 to 3 and on clip 2 the idle would hang for a little while before comming down.



i had the same off-idle bog when whacking the throttle open to wheelie something. thought it was my jetting (which it partly was)...but also noticed that my bk mod screw moved in (the loctite didnt hold) and my squirt duration was reduced to near nothing. upon setting it back to 0.5 seconds, and slightly changing my jetting, the bog went away! didnt change my jetting all that much from when i had the problem, so i believe it was just a lean condition at low revs and the fault of the bk mod screw moving on me.

good luck!

I think the pump timing is off. Seem to have a delay, not even close to hitting slide.

Which way do you turn the adjuster to speed up the pump timing?


you really should not touch that.

If you do be very diligent to count the turn cw or ccw.

The pump has nothing to do with direction of the squirt, it deals only with the timeing of the squirt.

Maybe I miss understood, but it is not wise to adjust this at all unless its blatently out of time


not sure which way you need to turn to adjust it from hitting/not coming close to hitting the slide. just experiment. i personally didnt have to adjust it at was already just barely missing the slide as it moved up out of the way. some folks had to adjust it because it was hitting the slide on the way up. never heard about the other side of the coin (like you have), but i'm sure that you can adjust it back. i'm also sure that being that delayed, you're getting a lean condition at first...then lord know's what after the spray starts to fly!

anyway, good luck! let me know if there's something else i can help with!


That's exactly why I used the P-38 Lightning on my YZ when adjusting the pump....Took all the guess work out that I had with my WR.

Bonzai :)

I had same problem with 02 but who cares where b-k is if you can stab the throttle and it rocks,turn it till you like and RIDE!my jetting is very similar to yours and i just backed out till it did not bog.Do you have a spring/thread lock on it to keep it stable?I adjust mine depending on altitude,heat,humidity seems to work,do you have a kouba-t i also fiddle with that and usualy can get the bike to run awesome and with that jetting great gas mileage also.But i must admit i am no garret berg and am just in the begining stages of carb @#$%@$^! :)

The BK mod added a screw to control the duration of the squirt, there should have been another screw on the same little cam thing that controls the start timing. You need to adjust that one if it's lagging too far behind the slide.

Your jetting setup is very similar to mine, but based on my recent experience dialing my "Taffy" jetting your pilot looks too big and your compensating by dropping the needle to lean out the bottom. My bike would not run very well on the bottom end with a 38 pilot after switching to the EMM needle.

If it was my bike I would straighten out the pump timing, then get the PJ/PAJ optimal, then verify clip pos'n. I am bog free with the following:

I'm @ sea level, 55-65 degrees, average humidity






~.5s squirt


Bog update:

Tried adjusting the pump timing but things just got worse. So I went back to the stock setting.

The 35pj & pas came in so I set the pas at about 50 and moved the emm clip from 3 to 4.

Bog has all but gone away. Runs good all the way to the top but did notice that it was running a little hotter than normal.

Anyone runing this jetting having trouble over heating?

I may try to change the needle to clip 5.


I think that your problem when you had the accel pump mod screw in was with the timing screw. I had the same problem when I first did the mod. I adjusted my timing to cure the problem. if you do this.....realize that moving the timing screw will affect the spray duration. Every time you move the timing screw, you need to re adjust the limiter screw that you installed to attain your desired spray length.

My spray barely misses the slide when the throttle is opened. it will slightly hit the slide if it is opened very slowly.

Hope this made sense and I hop it helps.

Just like with YZ timing, the leaner jetting did make my bike run hotter. Hot enough to spuy So I'm not worried. Nor is it hot enough to cause detonation (ping).


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