BK Mod Gone Bad?

12 replies to this topic
  • cowboyona426

Posted April 12, 2002 - 06:15 PM


After I got my bike put back together after checking valve clearance and doing the BK Mod, I was excited to see how the BK Mod helped. Turns out it didn't!!! I still have that damn bog when I open it wide! How far should the screw be turned in to stop the accelerator pump cam? I looked at Motoman's web site, and I had to turn my screw in WAY farther than his is in the pics just to make it contact the cam. Any help would be appreciated.

  • Eagle426

Posted April 12, 2002 - 06:40 PM


What year is your bike? I have a 2002 and when I did mine, the settings looked nothing like the pictures posted. I just tried different adjustments until I got the spray and duration that I was looking for. If yours in an 02, this makes mw wonder if the 02 carbs are slightly different from the previous years!

  • cowboyona426

Posted April 12, 2002 - 06:43 PM


Mines a 00, but the carb is still the same I think. It may be a jetting problem, but I don't think it is. Worth a try though.

  • F-Pilot

Posted April 12, 2002 - 07:15 PM


You may need to adjust the timing screw to get rid of the bog. I was never able to completely eliminate it but it was alot better.

  • John_Lorenz

Posted April 13, 2002 - 03:35 AM


I have an 00, With a W/Bros R4. Aftre I put the Bk in I still had a slight Bog off bottom. I ended up the the final jetting to get rid of it. Now the bike snaps. (Note Main veries for me)

Pilot 45
Main 165 -- 168 depends on Day's weather
Dropped the Needle Clip One down (This raises the Needle.
Air Screw out 1-3/4 turn

Also make sure the carb is well cleaned to

  • cowboyona426

Posted April 13, 2002 - 07:09 AM


How bad is the bog on your bike Ego? When I COMPLETELY open the throttle with the bike idling, it will actually kill itself. I'll have to double check my jetting, but I'm pretty sure I'm running a 168 main- stock pilot and stock needle clip position, fuel screw is about 2-3/4 turns out as per FMF after the installation of a PowerCore IV. How much should the BK Mod limit the accelerator pump cam movement? Thanks for all the help, keep it coming!

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • acarter920

Posted April 13, 2002 - 09:11 PM


Remember... a too rich engine will bog, but, an engine that doesnt get enough gas will bog also. Best advice i can give is just to keep messin with it until you get that .3 second (i think) squirt. Once you have that down, then start messin with the fuel screw. If that doesnt help then try leaning out the pilot jet circuit.

  • John_Lorenz

Posted April 13, 2002 - 11:31 AM


Throw a 45 pilot in it the screw should not be that far out only 2 turns max

also raise the needle one clip (Drop the clip one)

This should do the trick for you

  • Mark_Cantrell

Posted April 13, 2002 - 12:15 PM


It may not be the squirt. I run stock pipe with either no baffle, stock baffle, or vortip. With either the stock baffle or Vortip, I have a big bad bog down low. Without a baffle, I have no bog at all, revs right out of idle.

First thought is accel pump and either BK or P38, right? But if I go fairly slow like 10mph in 5th gear and give it any amount of throttle over what is required to hold it at that speed, the bog comes and stays. Way after the AP squirt (mine is just under 1 sec stock) has worked its way through, as long as the RPMs are low, I've done it up to 30sec anyway. Note, happens at all throttle positions, long after squirt is behind me in the fumes.

So I am having trouble believing the AP is involved. I went out today and moved from 170main, 42 pilot, 1 5/8s out, OBELP #3 to 165, 38, zero out, OBELP#1. The idea was to make it real lean everywhere. The bike is snappier (and pops all the time) but the bog is still there (running Vortip today).

I am convinced it is ignition timing or cam timing (was running Vortex in power mode). I may try WR cam timing.

Are my conclusions about not being jetting (all throttle positions) and not being AP (bog lasts as long as RPM are low) correct?


  • RichB

Posted April 13, 2002 - 12:19 PM


I haven't had time to do the BK yet and now that I've tinkered with my jetting I'm not sure I will. Worst case, set you carb back to stock settings and get your jetting as close to spot on, then fiddle with the spray duration/timing.

I know a lot of folks are going richer, expecially with the clip position but going 1 step leaner on the needle helped mine out like you wouldn't believe. I can low speed wheelie now with no bog whatsoever.

Look at the jetting .xls chart on motomans web page and start there. Also, like said above, make sure the carb is clean, your air filter is not too oily and you're using a consistent fuel source. My air screw is all over the map depending on the temp/elevation but I'm using the stock pilot, clip is 1 leaner, and I switched the top end jetting to a 165 using the pipe I have.

Good luck.


Posted April 13, 2002 - 02:45 PM


What happens if you cut every wire going to the carb?

  • cowboyona426

Posted April 13, 2002 - 06:10 PM


Then its time to get a new TPS MX! Unless you cut them up higher, then you've got real problems.

  • Mark_Cantrell

Posted April 13, 2002 - 06:41 PM


There is only one wire going to the carb, the Throttle Position Sensor. It is only used to change the ignition timing. The wire goes from the carb to the CDI (ignition control unit) that uses the RPM and throttle position to determine the spark advance.

It would run worse, but it would certainly still run.


Related Content


2016 YZ450 by CaptainKnobby

Dirt Bike   Dirt Bike Technical Forums   Suspension
  • Hot  59 replies

James Stewart back on a YZ450F by YamaLink

Dirt Bike   Special Interest Forums   Pro Racing
  • Hot  47 replies

Wilson the Blue Privateer by jetfuel

Dirt Bike   Special Interest Forums   Pro Racing
  • Hot  50 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

Michigan Motocross Tires by 288yz450

Dirt Bike   Dirt Bike Regional Discussion   North
  • 1 reply

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.