Bk mod question

3 replies to this topic
  • Airhawg

Posted December 17, 2001 - 04:28 PM


I've been a lurker here for about eight months. This place is great!

Okay, I have gone over most of the past posts on the BK mod and I finally did the mod just the other day. I just need some validation on a few things.

I have a 2000 yz426
Main jet 162
Needle clip five from the top (was at four before mod.)
Fuel screw @ 1.75 out
Pilot jet stock @ 42
Elevation 7000'
BK squirt @ .35 sec

Question: Before and after the bk mod I noticed that when I blip the throttle fast from idle (while in neutral)it will stall the motor. If I get the rpms a little higher and then blip it fast it will rev fast with no bog.

As an experiment I adjusted the bk screw so NO fuel at all squirted into the carb. Again blipped throttle hard and it still would die.

Should the bk mod eliminate ENTIRELY the stall tendancy if its done right?

I'm fairly new to the sport so please keep answers specific and in english.



  • Hick

Posted December 17, 2001 - 05:31 PM


Why do you care what the throttle response in neutral is like? When you whack the throttle open with no pump the motor starves and dies before any fuel can make its way through a jet and into the venturi. Try a few quick roll-ons in first or second gear and try and eliminate the bog you get with the pump all the way on.

To get the most out of the BK thing most people end up with additional pump timing delay (the other screw by the pulley that came stock on the carb, in is more delay). I have ¼ or so over stock on my ’00 and ’01 w/ about 1 mm of pump stroke, measured at the rod.

Also, how cold is it up there? I ride at 4k feet and I just now went from a 40 to 42 pilot and from clip # 3 to # 4 as daytime temps fall into the 50s.

Finally, if you still have the stock ’00 needle you may benefit from the stock ’01 needle or this alternate ’00 needle which is one size leaner, 5JG-14916-E1, especially in the winter.

Hope this helps.

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  • Fastest1

Posted December 18, 2001 - 07:13 AM


Why not raise the idle also it will make you coast through corners faster. We used that trick in roadracing, we set idles around 2000rpm at least. No stalling. Carburetors need a good signal(vacuum) to perform correctly. They do not get much vacuum at a low idle. Good Luck Cya

  • F-Pilot

Posted December 18, 2001 - 01:45 PM


Ditto on Hick's advice.
You need to work with the timing screw now. After I did the mod I had adjusted the squirt timing to just miss the slide and was getting the same problem you have. It took 1/2 to 1 turn in on the timing screw to eliminate the bog/stall.
You'll never be able to just whack the throttle open on the stand but it will be better than before.
The on track improvements are what counts.

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