BK mod notes & how to



22 replies to this topic
  • TeamScream

Posted September 03, 2001 - 09:05 PM

#1

I just finished the BK mod (actually did it @ 12AM this morning) and I wanted to share my notes with a few of you who may be a little sketchy about drilling and tapping your carb. This is the best mod I have done so far to improve the useability of this bike! and the total parts cost was around $13.00 and EVERYTHING can be purchased from Home Depot 24 hours a day! (in most areas) PLUS the coolest part is it takes less than an hour to do.
Heres what I did step by step:

1)Go to Home Depot (11:00 PM 2 miles from home) buy a 6/32 NC tap w/correct drill (7/64) for the job(they come together in a pack made by "Hanson" for $2.89), also had to ge tthe tap handle $3.89, A small pack of 1" 6/32 machine head screws for $1.49, also a small pack of #6 washers (they opnly had the jumbo pack) $2.00 and a package of "handyman" springs (same isle as the screws part # SP-9700 made by "Prime-Line") $3.00, All total I spent $18.00 but that was because they had a 2 can special on WD-40 in a big box at the checkout stand for $2.89, and i'm a sucker for specials like that. (Jam Home)

2) remove seat/gas tank

3) remove coil (makes it easier to get at the cables)

4) remove throttle cable cover and unhook throttle cables

5)pull the octopus out of its cage and disconnect fuel line

6)loosen screw and allen bolt front and rear of carb and remove carb out the left side of the bike by pulling backward on the airfilter side of the rubber boot.

7)look in through the rear of the carb and rotate the cable wheel and count 'one one thousand-two one thousand" etc...etc... till the gas stops squirting (if you are anything less than about 4-5 seconds you may very well be the first one ever) mine was a little more than 5 seconds!

8)drain the gas out of the carb or it will spill on your garage floor and stink when you work on it (just tilt it sideways over a can or something)

9) mark the spot where you will drill the hole with a pencil then center punch it lightly to guide the drill

10) tape of stuff rags into the front and rear of the carb to keep the drill shavings out of the critical areas

11) but a amall piece of wood or plastic to tape into place so you dont drill to far and damage the little accelerator pump arm, then DRILL THE HOLE.

12) tap the hole (use a little WD-40 to keep the hole nice and tight) then blow off the chips and crap (or use a paint brush if you dont have air)

13) take one of the springs and stretch it slightly till it measures roughly 3/4" (they are 1/2" out of the bag)then take one of the screws and put a #6 washer on it, then the spring, then another washer, and then put this setup into your nice new hole.

14)Set the gas tank back on the bike and hook the carb to the fuel line and fill the carb back up with gas

15)now go outside (gas will squirt) and rotate the throttle cable wheel again and count, then turn the screw in a little bit at a time till you get below one second total squirt duration (actually .3 to .5 sec's), also look at when the squirt happens...it aparently needs to happen just after the slide lifts out of the way, so I adjusted the timing screw to make it that way (didnt take much adjustment) then I checked and re-checked the squirt duration and timing, I also went back after about 10 squirts and filled the carb up again to make sure there was no "low fuel" error, and rechecked it again.

16)Inspect EVERYTHING and make sure no dirt, debris or kaka got into anything then put a small drop of locktite on the front of the screw so that it wont vibrate loose (or tighter) and put the carb back on the bike and buckle it all up (reverse the removal proceedure outlined above).

17) I had to go to bed (it was midnight) BUT I was up at 8:00 am and ready to try it out....OH MY GOD!!!!!!!!!!!! the bike started first kick with the choke, and I could immediately tell there was something WAYYYYYYYY better about it, after letting it warm up I took it for a spin around town (heheh mine is CA licensed) this is HUGE!!!!!!!! it has so much better throttle response and pulls so much harder through low to mid range that I am completely BLOWN AWAY!
YOU NEED TO DO THIS MOD, it will change the way you look at your bike, it is a MUST do mod.....thats all I can say.
I hope this helps the newer guys (like me) who are a little aprehensive about tearing into your machine, even if you are a little less than mechanically proficient this is a really easy mod to do, the hardest part of the whole thing is not squirting yourself in the eye with gas cause you looked into the wrong end! (heheheh joke)
....let me know how it go's!

Dauv

  • motoman393

Posted September 03, 2001 - 10:05 AM

#2

Congrats, I know the feeling!

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I get my kicks on a 426!
Motoman393's MX Site

  • benny_d

Posted September 05, 2001 - 06:36 AM

#3

This post gave me the confidence to try this yesterday. I did and could definitely notice a difference even though I cannot ride the thing because I have a paddle tire on it. I am going to change it to a dirt tire tonight and really test her out. Such an easy mod to do, and fun!! Thanks to all that have contributed to this topic.

  • TeamScream

Posted September 05, 2001 - 07:00 AM

#4

Right on Bro!
I am glad I could help (finally) it is easy and definately makes a difference, I am doing some jetting experimenting today and last night as I had the carb off I noticed the timing of the squirt was off a little, when i rotated the cable wheel the squirt didnt start till the slide was up a little bit (about 1/3 up) so I adjusted the timing screw again and got it to squirt almost exactly when the slide clears the stream, throttle response seemed to improve even more!, keep an eye on it!

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01' WR426,YZ timing,EMM #5,#48Pilot,#100PAJ,#168 Main,BK mod,stock pipe-no baffle, open airbox,Gray-Wire,K&N, throttle stop mod,CA Street Legal (sort of) Pure Super Motard w/17 in. wheels, 15/46 gears,ProTaper bars,

  • SUnruh

Posted September 05, 2001 - 07:22 AM

#5

i did the "BK" mod to my carb yesterday morning as well for the fun of it.
the squirt didn't hit the slide and the duration was less than 1 second because i couldn't even count to 1 before it had stopped. so, the Factory R&D P-38 Lighting i've had on the bike for several months must be doing its job. i fiddled with it some and rode it and there is no difference on my bike. i had the tap and the drill bit already. the screw (from Tractor Supply) at .49 and the spring from my yamaha dealer was .29. under a single dollar and just time. if you have the stock pump cover, the cheapest fix (besides cutting the grey wire on a wr250f) you can do.

  • TeamScream

Posted September 05, 2001 - 08:24 AM

#6

Totaly agree that it can be done WAYYY cheaper than I did it for but keep in mind, it was 11:00 PM at night, most people were in bed already and there certainly werent any hardware stores open. The only choice i had was Home Depot which is open 24 hours in my area and unfurtunately they only sell things like screws, washers and springs in nice pre packaged little bags, not single items at all, and I am sure I had the tap laying around somewhere but I couldnt find it so buying a new one for less than $3.00 was a no brainer, and since I was jacked up on caffeine and couldnt sleep it was well worth it to do it on a Saturday night at almost midnight! I am sure youve been there!

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01' WR426,YZ timing,EMM #5,#48Pilot,#100PAJ,#168 Main,BK mod,stock pipe-no baffle, open airbox,Gray-Wire,K&N, throttle stop mod,CA Street Legal (sort of) Pure Super Motard w/17 in. wheels, 15/46 gears,ProTaper bars,

  • Brett_Green

Posted September 06, 2001 - 12:24 PM

#7

This BK mod all sounds interesting.

Is the same true for a UK bike or is it just US specs?

More importantly, where do I drill this hole?????

Brett

  • TeamScream

Posted September 06, 2001 - 04:06 PM

#8

the hole gets drilled on the little flat spot of the carb body which is right behind (air filter side) the Accelerator Pump actuator arm which is just below the cable wheel. the hole needs to be centered so that when you put the screw in place it is fairly centered over the actuator arm. Its almost as if Kehin was going to do this mod themselves then forgot or something....all the amenities are there including the mold mark on the plactic cover that you have to cut to clear the screw if you do this mod.

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01' WR426,YZ timing,EMP #5,#48Pilot,#100PAJ,#172 Main,BK mod,stock pipe-no baffle, open airbox,Gray-Wire Pulled,K&N Filter, throttle stop mod,CA Street Legal (sort of) Pure Super Motard w/17 in. wheels, 15/46 gears,ProTaper bars,

  • WR_Jason

Posted September 07, 2001 - 05:53 AM

#9

What dose the screw do? What year bikes dose it pertaine to and why?

  • Thumper33

Posted September 07, 2001 - 10:20 AM

#10

This only works on 426s right? Why doesn't it work on 400s?

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2000 WR400F - Throttle stop shortened, Grey Wire Cut, Filter Cover Removed...

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  • James_Dean

Posted September 07, 2001 - 10:34 AM

#11

Thumper33,

The BK mod works on any '00 or newer WR/YZ thumper model Yamaha. Yes it will work on your '00WR400.

  • benny_d

Posted September 07, 2001 - 10:41 AM

#12

I think it is really weird how there is a spot that is made for this mod. I really do think they were going to put a screw there. The cover cutout marks really make that apparent. I wonder why they did not just put one in.

  • funktree

Posted September 09, 2001 - 03:33 PM

#13

Does anyone have pictures of this mod? Im pretty sure I know where the hole gos but I would like to see a picture. So far every mod Ive done to my bike Ive managed to screw up somehow.

  • Stefe9999

Posted September 09, 2001 - 03:40 PM

#14

This ought to show you what you need http://mx393.tripod.com/carb.html

  • funktree

Posted September 09, 2001 - 05:46 PM

#15

wow good pics thanks. You got it from every angle and then some.

  • InSpace

Posted October 11, 2001 - 05:52 AM

#16

TeamScreamm.....

Thanks.... did the mod... as suggested last weekend... at 12:00am... thank god for Home Depot...

  • BlueThunder

Posted October 11, 2001 - 07:56 AM

#17

Why is it that motoman393's site claims that the BK mod does NOT apply to 99-00 WR400's ?
I haven't done the mod due to this info, yet the master JD says it applies to my Y2K ?
Someone please clarify so I have a project to do tonight. Prepping the beastie for a hard weekend Posted Image.

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Y2K WR400FM,Answer top tree w/Accu-Trax clamp,Pro-Tapers(CR-Hi w/ EE handguards),Devol Rad. & frame guards, Guts tall soft foam w/ ballistic cover, 14/52 w/DID VM X-Ring, Kouba-T,Michelin M-12's ft.& rr.,12 oz. flywheel weight, Zip-Ty Racing Link & Shark Fin(plus everythhing else cool that Ty offers), Cycra front rotor guard and T.M. Designworks Chain guide, buffer & chain wheels. Street legal except for the non-"DOT" tires.

  • Taffy

Posted October 11, 2001 - 08:11 AM

#18

you can do it to the Y2K you can't do it to 98/99.

Taffy

  • BlueThunder

Posted October 11, 2001 - 08:34 AM

#19

Thanks Taffy.....Any idea why Motoman393's site reads different ? Seems to be a pretty
accurate site other than the applications for the BK mod? You gonna try to convince me to disconnect the AP ? Don't know if I can part with the little squirt yet because I'm a wasteful American through and through..." bigger is better and TOO much is NOT enough!" Posted Image More gas means more power......right? Posted Image

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Y2K WR400FM,Answer top tree w/Accu-Trax clamp,Pro-Tapers(CR-Hi w/ EE handguards),Devol Rad. & frame guards, Guts tall soft foam w/ ballistic cover, 14/52 w/DID VM X-Ring, Kouba-T,Michelin M-12's ft.& rr.,12 oz. flywheel weight, Zip-Ty Racing Link & Shark Fin(plus everythhing else cool that Ty offers), Cycra front rotor guard and T.M. Designworks Chain guide, buffer & chain wheels. Street legal except for the non-"DOT" tires.

  • TeamScream

Posted October 12, 2001 - 09:15 PM

#20

Good Job blue Thunder!
Isnt the 24 Hour home depot a great thing?
I love the fact that I can go get just about anything I need at midnight if i want to....
COngrats on teh BK Mod!

Dauv

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01' WR426,YZ timing,EMP #2,#48Pilot,#100PAJ,#175 Main,BK mod,Kouba T-Handle,YZ pipe, open airbox,Gray-Wire Pulled,K&N Filter, throttle stop mod,CA Street Legal,Pure SuperMotard 17 in. wheels, 15/46 gears,ProTaper bars,




 
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