KL (BK) mod

13 replies to this topic
  • Guy

Posted November 25, 2001 - 10:29 PM


Hi there, can anyone tell me if doing this mod will be affective for a UK bike or is it a US only mod like the grey wire???
I'm kinda new to this 4 stroke business and I don't want to Bollox up my bike if it is not ness for mine
My bike is a '99 WR400

[ November 25, 2001: Message edited by: Guy ]

  • MN_Kevin

Posted November 25, 2001 - 12:14 PM


Your bike will benefit if your Accelerator Pump Jet [APJ] needs adjustment.

Your squirt duration should be set to < 0.5 seconds,


the squirt should not hit the slide valve [APJ timing].


  • Guy

Posted November 25, 2001 - 12:52 PM


:) Thanks for that Kevin....I'll try it out and see where I get to :D

  • Guy

Posted November 25, 2001 - 01:21 PM


:) :D Just re-read your thread re the mod and there is one more thing.....any chance of translating the drill sizes and bolt sizes into either "imperial" ie 1/8 dril etc or "metric" as a #43 drill bit don't mean a thing to me!! :D :D

  • The_Missile

Posted November 26, 2001 - 05:17 AM


BK mod is NOT for 98 or 99 but for 2000+ models. What makes the BK mod inapplicable on the 98 and 99 is that the tab that you drill out & tap is inexistant.

For 98, 99 models there are 4 options

- remove apj activity altogether (see taff timing & jetting)
- BK mod with alternative support bracket (recently posted)
- p38 lightning - replacement gizmo
- KL mod tapping the apj cover with an adjustment bolt/nut

tapping the apj cover: adjusting the diaphragm movement by blocking it with an adjustable screw you fit in the tapped apj cover.

'bracket' mod : was used to hold the bk apj "stopper". Recent thread covers this, even with (terrible) photos.

A coupla minutes with the search function should find it for you.
here is the thread...BK(KL) mod
but I guess you already new that as you referred to above I now realise....am I confused or WHAT??

[ November 26, 2001: Message edited by: The Missile ]

[ November 26, 2001: Message edited by: The Missile ]

[ November 26, 2001: Message edited by: The Missile ]

  • Guy

Posted November 26, 2001 - 07:43 AM


:) I'm glad it's not just me who is easily confused... LOL! No as you have gathered I had already sussed that it is the KL mod I need for my bike ..I reall just wanted to confirm that it was applicable to my UK spec WR and not just the US ones.
Thanks anyway though :D :D

  • MN_Kevin

Posted November 26, 2001 - 09:30 AM


I will be consulting my mechanical book to give you the metric equivalents.

Also, the P38 by itself WILL NOT set your AP timing.

[ November 26, 2001: Message edited by: NH Kevin ]

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

Posted November 26, 2001 - 01:44 PM


:) Kevin, it may not be needed, I have spent the evening in the garage pulling my bike into a million bits (well it seemed that way any how) and having observed the timing of the jet and duration my pump just misses the slide on its way up and the duration seems to be about.75 to .85 sec's..it's a little difficult to hold the torch,turn the throttle and use the stopwatch all at the same time he he he!!
From reading your thread it would seem that this is certainly in the correct area not in the 5 sec duration that some others seem to have had!
Thanks anyway for your time and if the above seems wrong just post back :D :D


  • MN_Kevin

Posted November 26, 2001 - 02:50 PM


Your numbers are a lot less severe than some I have read. My squirt duration was about 2 seconds.

I don't know how much you would gain by lowering squirt time to < 0.5 seconds.

I guess if it works OK...

UNLESS you are bored :)

[ November 26, 2001: Message edited by: NH Kevin ]

  • Guy

Posted November 27, 2001 - 09:51 AM


:D Hmmnn..... I'm not that bored yet :) but who knows if we end up with lots of snow I may just do it..HE HE!
Thanks again


  • Joel_Gibson

Posted November 27, 2001 - 12:58 PM


What kind of adjustment would be necessary with the P38 on a 98 WR400?

  • MN_Kevin

Posted November 27, 2001 - 01:28 PM


I do believe I have the metric version of this.

The tap is M3 x 0.5 using a 2.5 mm drill bit. Before you go crazy and start drilling holes all over your bike :) , try to verify this through a machine shop.

In the States, we have a chart we use. It displays the desired bolt and pitch, then gives you the tap to use, and the drill bit required for the tap.

  • MN_Kevin

Posted November 27, 2001 - 01:33 PM


There are 2 distinct areas to cover w/ this mod, (or w/ the P38 as well).

1 - The APJ timing


2 - The APJ Volume (or duration of squirt).

I thought the P38 just deals w/ duration, not the timing...(???)

I hope all your answers are in this post. If not, just ask. :)

  • Guy

Posted November 28, 2001 - 10:40 PM


:) Kevin you are a star! The sizes sound right to me based on previous drilling expeditions! :D BUT I will verify that they are OK before the Swiss cheese appears on my bike LOL :D
Thanks again for your time it is much appreciated


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.