06WR450 BK mod pics


20 replies to this topic
  • Fullbore4

Posted November 26, 2006 - 02:56 PM

#1

For those who have the new style Keihin carb, here are some pics of a screw I inserted per the BK mod listed in Performance Mods thread (http://www.thumperfa...e_mods.htm#WRF). I used a 10x32NF bolt 1 inch long and a spring I had in the mess jar. The leak jet is plugged off and the AP timing is set per my service manual. I didn't take off the sub frame and time the squirt as I just carried a small wrench and adjusted until I liked it. I found it works best with a 1 mm gap between threaded bolt end and push rod cam.

Doing the AP mods greatly improved my throttle response. It has snap like my old YZ 250 and has no bog, hesitation, stutter, etc. It takes a little thought to drill and tap the cover plate but can be done on an 06....very cheap mod too.

http://i115.photobuc...ModScrew001.jpg

http://i115.photobuc...ModScrew002.jpg

http://i115.photobuc...ModScrew003.jpg

http://i115.photobuc...ModScrew004.jpg

http://i115.photobuc...ModScrew005.jpg

http://i115.photobuc...ModScrew006.jpg

  • TD-3

Posted November 26, 2006 - 03:12 PM

#2

Awesome job :worthy:

I did the same to mine, instead of a spring I used a nut to lock the bolt against the cover. Your's looks very easy to adjust once installed. Another side effect of fine tuning the AP is improved gas mileage.

  • Just_a_trail_rider

Posted November 26, 2006 - 06:42 PM

#3

Improved throttle response....

thats something we all like. But I don't fully understand what's going on here. Can you break it down in simpler terms? I don't know what the leak jet does? I only know about the pilot, main and needle.

  • Fullbore4

Posted November 26, 2006 - 07:44 PM

#4

Improved throttle response....

thats something we all like. But I don't fully understand what's going on here. Can you break it down in simpler terms? I don't know what the leak jet does? I only know about the pilot, main and needle.


I gleened all my info from reading on that thread I included in the post which is why I left out details. The leak jet allows part of the fuel that leaves the AP to go back into the bowl instead of into the carb throat. What I have done is gain complete control of what the AP does as far as "squirt duration". Notice AP squirt timing (when gas starts being sprayed upon whacking the throttle) is adjusted per the Service Manual. Please read on that thread provided under "Accelerator Pump Modifications" under BK mod and HB/Doc mod......then I can clarify what you don't understand.

  • MountainMax

Posted November 27, 2006 - 05:19 PM

#5

what is a BK mod, i couldn't find it listed in the link you posted.

  • Fullbore4

Posted November 27, 2006 - 05:42 PM

#6

scroll down to Accelerator Pump Mods in that link.....man you guys are missing the meat and potatoes of this site.

  • MountainMax

Posted November 27, 2006 - 05:46 PM

#7

ok, why is it called BK mod and what does it do?

  • clark4131

Posted November 27, 2006 - 05:56 PM

#8

Not to burst your bubble, but the BK mod is unnecessary in the new generation of Keihin carbs. An less invasive method is to adjust your duration by changing out your AP diaphragm for one with a longer stud. Don't get me wrong, you did a nice job and it is both cheaper and adjustable, where the diphragms can get spendy and it's not a "one size fits all" remedy like yours. I did an extensive bit of research into this and came up with a bunch of different durations based on multiple combinations of leak jets and diaphragms. I posted the link to my findings in the Performance Index...SC

  • Fullbore4

Posted November 27, 2006 - 05:57 PM

#9

google "BK mod". It was derived by a factory mechanic I believe......but on the 06 they changed the cover plate which makes it hard to do. Hence i posted pics to give others an idea. I believe lots have done it in various ways. It is a way to gain control of spirt duration when you whack the throttle. I am too lazy to rewrite what others have done but since its winter, I hope you'll find the time to explore. On that link I provided is other mods that'll crank out the hidden horses in a WR.

  • Fullbore4

Posted November 27, 2006 - 06:07 PM

#10

Not to burst your bubble, but the BK mod is unnecessary in the new generation of Keihin carbs. An less invasive method is to adjust your duration by changing out your AP diaphragm for one with a longer stud. Don't get me wrong, you did a nice job and it is both cheaper and adjustable, where the diphragms can get spendy and it's not a "one size fits all" remedy like yours. I did an extensive bit of research into this and came up with a bunch of different durations based on multiple combinations of leak jets and diaphragms. I posted the link to my findings in the Performance Index...SC


Well I don't claim to be promoting any big break through.

I've read about changing diaphrams and stuff but why not be able to ride and test and adjust in a few minutes and have "ADJUSTABILITY" (as you mention) for a few bucks. Yah one has to have a little luck getting the angle of the screw close but there is margin for error and if need be a new cover plate can be had for 16.95 at JT parts if you plain mess up the one you have.

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • Fullbore4

Posted November 27, 2006 - 06:33 PM

#11

Max I did the bk mod months ago but just took my carb off lately and got a new dig camera ta-boot. Re-looking at that one particular thread, it doesn't have too many more mods that crank out the extra horses that you probably haven't done yet.

I know my bike rips but other's WR's prolly do too so I can't compare.

  • Matt96xr6

Posted November 27, 2006 - 06:46 PM

#12

Why the hell would you do this? STUPID!

The reason the BK mod was used was for the 00-02 YZ426 ONLY! The 426 did not use a leak jet in the carb bowl. Thus no way to limit your duration easily.

All the YZ250Fs and all the YZ450Fs have leak jets in them. This is WAY better and much more adjustable then the BK mod. Plus no screwing with the carb.

  • snowman02

Posted November 27, 2006 - 07:07 PM

#13

I have been doing alot of reading on this BK mod. Now please give me some info on what i am about to ask. Now the Boysen Quick Shot, isn't that basically doing the same thing as the BK mod is doing to the fuel. I thought under my interpitation that the Quick Shot takes fuel hesitation away? Now if i am mis interpiting something please let me know, and if they do two different things to the fuel system i would like to know what differences they are. Sorry for the stupid questions, i am just trying to sort all this info.:worthy:

Thank you

  • snowman02

Posted November 27, 2006 - 07:11 PM

#14

I have been doing alot of reading on this BK mod. Now please give me some info on what i am about to ask. Now the Boysen Quick Shot, isn't that basically doing the same thing as the BK mod is doing to the fuel. I thought under my interpitation that the Quick Shot takes fuel hesitation away? Now if i am mis interpiting something please let me know, and if they do two different things to the fuel system i would like to know what differences they are. Sorry for the stupid questions, i am just trying to sort all this info.:worthy:

Thank you



Ohh yes, and i have a 02 WR426, so if these two mods are different which route or both routes would be best?

  • Fullbore4

Posted November 27, 2006 - 07:42 PM

#15

Ohh yes, and i have a 02 WR426, so if these two mods are different which route or both routes would be best?


I would do both routes since they cost nothing and then you have complete control of squirt duration. The boysean is for keeping the ap full and delivering instant squirt. Please read the info in the archives to get a full understanding and to avoid other caveats that lurk in the shadows. I don't intend to rehash them all here.

Max96xr6.....what is the duration on your biike in seconds and how far does it squirt? Also which combination of leak jets, push rod and other parts do you get best results with?

  • Matt96xr6

Posted November 27, 2006 - 07:47 PM

#16

Again, the BK mod only works on the 426 Yamahas. WRs and YZs.

Why? cause they dont have a leak jet in the carb.

The Boysen quickshoet and other covers will not cure any jetting issues. They dont change ANY jets. You need to jet the bike properly. waste of $80 there.

So for the 426 bikes, do the BK mod.


For all other bikes use the different sized leak jets available to you.

  • Fullbore4

Posted November 27, 2006 - 08:25 PM

#17

One thing about these mods is you might have to adjust the ap timing so the squirt doesn't hit the slide upon whacking the throttle because with these mods, you have an instant squirt of gas with a duration that is now set by the bk mod screw. Both DO NOT require removing the carb. Just a simple adjustment on the side of the carb.

  • Fullbore4

Posted November 27, 2006 - 10:30 PM

#18

Just one more note after going back and re-reading part of that thread that I put in my first post. Very competent mechanics spell out exactly what I've done on>>>>> 03-06 models <<<<<< too.

The only thing I've added to their words and efforts is to provide a few pictures because they weren't available when I did my mods months ago.

Mr. Clark I have read several of your efforts and I do respect your input.

  • TD-3

Posted November 28, 2006 - 04:08 AM

#19

Why the hell would you do this? STUPID!

Nice reply

All the YZ250Fs and all the YZ450Fs have leak jets in them.

Again, the BK mod only works on the 426 Yamahas. WRs and YZs.


Well, I have a 03 YZ450 and I can guarantee it DOES NOT have a leak jet in it. This version on the BK mod is well documented on the web and works great. For the 1/2 hr and $.25 it takes to do the mod it's kind of a no brainer. It is 100% adjustable, where as a $30 diaphragm (with no leak jet) is not.
Once again, great job on this simple, inexpensive, adjustable mod. It's awesome to adjust the AP squirt duration without having to remove a thing from the carb. :worthy:

  • mtrablue

Posted November 28, 2006 - 05:17 PM

#20

a bit of history; BK is for brian kinney (sp?). he was tim ferry's mechanic when he was with yamaha on the four stroke. it was not that unusual for the four strokes of that time to cough and die at any given time. sometimes too much squirt was as bad as not enough. he figured a way to adjust it. the BK mod.
the leak jet (if you have one) fine tunes the differance between diaphragm sizes. a fourty leak jet did the trick for my WR. for some, it's not enough. so what's the problem with trying different stuff? that's what this site was all about when it started. before there was the BK mod there was the Taffy mod. the older 400's had an exposed accelerator pump shaft. some owners would put a small coller with a set screw in it, on the shaft. it was used to limit the amount the shaft could travel and therefore adjust the squirt. what a pain in the ass that must have been!




 
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