BK mod - this time in metric



37 replies to this topic
  • Ron_in_SoCal

Posted October 14, 2001 - 02:30 PM

#1

Well, I just got done doing the BK mod using metric parts. The carb won't be going back on the bike until I get a few needles from Sudco tomorrow (while I'm there I'll get a 2 or 3 needles). Going to try the EMN needle with a 172 MJ and 48 PJ.

Before the mod, I was getting only about 1 second of spray. I took about half of that away with the newly installed adjustment screw. This should be easy enough to dial in one it is back on the bike. I'm sure I will have the carb off a few more times while dialing in the jetting so I'll mess with the adjustment of the pump as necessary.

Parts used:

1 ea. 4mm x 16mm "cheese head" screw with a .70mm thread.
1 ea. .25inch x .5 inch spring

Tools needed:
#30 drill bit (3.30mm)
4mm x .70mm tap
Tap handle

I will report how it works once it gets back together. The 16mm long screw seems to be the perfect length, and the spring has plenty of room to grow or shrink for adjustments. Check out the pictures below, although my camera's settings seam to be off a bit 'cuase they are find of fuzzy.

Posted Image
A freshly tapped hole in my carburetor.

Posted Image
Same hole with screw & spring.

Posted Image
From the side.

Posted Image
With notched cover installed.

Posted Image
Bag of ¼" x ½" springs as found at Home Depot.


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N 33'41.156" W117'59.749"
HelmetCam Videos

  • Ron_in_SoCal

Posted October 14, 2001 - 02:35 PM

#2

PS:
I know the springs are not metric. I looked but could not find them. Posted Image


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N 33'41.156" W117'59.749"
HelmetCam Videos

  • Hick

Posted October 14, 2001 - 03:01 PM

#3

I used the same Yamaha spring that comes on the timing screw.

PN: 5JG-14531-00-00

$1.12

  • John_in_Long_Beach

Posted October 14, 2001 - 03:34 PM

#4

I used a locking nut instead and a little lock tight. It isn't going anywhere, yet it is adjustable if needed.

  • John_in_Long_Beach

Posted October 14, 2001 - 03:34 PM

#5

I used a locking nut instead and a little lock tight. It isn't going anywhere, yet it is adjustable if needed.

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2000WR - EKN#5, 172MJ, 226MAJ, MAJ Passage drilled to 278, 48PJ, 100PAJ, YZ timing, BK mod, 3/4 turn pilot screw, DSP tapered header and pipe, IMS tank & YZ seat, Scotts dampener & triple clamp & Renthal Fatbar 971, White Bros suspension, Dunlop 756's.

  • James_Dean

Posted October 14, 2001 - 05:01 PM

#6

Ron,

Want a metric Spring?

While you're at Sudco get the pilot air screw spring- part#021-035 (~5mm x 11mm)

I used the same metric screw pitch, diameter, and length. (4 x .7 x 16mm)

This is a great picture to ask this question from. How much do you guys turn the upper delay screw IN from "touch point" to set the delay on the pump start?

If the upper screw is turned out, the gap is closed and the pump has no delay. The delay is somewhere between 1/4 and 1 1/2 turns in. You can feel the free play by pushing the linkage gently with a finger. When the rod touches the diaphram the linkage gets firmer/harder to turn. This is called the "touch point".

James

[This message has been edited by James Dean (edited October 14, 2001).]

  • Ron_in_SoCal

Posted October 15, 2001 - 03:40 AM

#7

James,

Thanks for the info on the spring. As for the delay, I'm at 5/8 turns in from touch point. This gets it to squirt just after the slide moves out of the way but seems to restrict the movement of the linkage. I'm concerned about how little the linkage moves.

Is it true that these carbs have a squirt duration of about 4 seconds in an unmodified state? I was experiencing only 1 second of squirt before the bk mod. Does this sound right? Now it is set for about a half second of squirt, and I will experiment with even shorter squirts once it's back together.


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N 33'41.156" W117'59.749"
HelmetCam Videos

  • Ron_in_SoCal

Posted October 15, 2001 - 05:22 AM

#8

I just spent that past hour reading up on all the jetting posts. I have to admit that I never really paid much attention to jetting once I got it dialed in two years ago. Since I'm off to Sudco in a few hours for parts I thought I would get educated. Ha!

Now I'm considering just leaving it be…

My neighbor John in Long Beach seems to have gone through all the trials and tribulations. Same year WR (literally, I almost bought the exact bike), same pipe, close in elevation (Glen Helen, right?) and temp. If I were to tinker with my jetting, why would I not use the same settings?

Hummm. John, are you now running a 175 main? Per your signature (thanks, btw), your specs are: EKN#5, 226MAJ, MAJ Passage drilled to 278, 48PJ, 100PAJ. This gives me a great deal of information on a starting point.

Why do I do this to myself?

  • James_Dean

Posted October 15, 2001 - 06:33 AM

#9

Ron,
Good question, the starting point helps a lot. I would not go any richer than 172, and most likely use 170-172 with EMN #4 or #5.

The spray was between 2 and 3 seconds on my stock carb. After the BK mod, .5-1 seconds.

An adequate delay(top screw) is important to reset the pump (refill) when the throttle is rolled off and back on to touch point. Usually 3/4-1 turn was enough, maybe 5/8 is OK.

  • Ron_in_SoCal

Posted October 15, 2001 - 09:03 PM

#10

Thanks again James. I'm going to follow your advise.

I just got back from Sudco with two EMN needles (maybe one for Khris?) and a cornucopia of jets & dodads. Thought that since I was at the Mecca of carb parts I should stock up They never heard of a EKN needle so I did not get one. Posted Image

Picked up a pilot air jet screw(?), main jets 170 - 175, a 200 main air jet (as large as they come? What's up with a 278?), and a few extra pilot jets to add to the collection of parts to work with.

I'm starting to "re-jet" my wonderfully running wr400 (why?) using the EMN#4 & 172MJ. I'll leave everything else (except for the bk thing) alone. Here goes…

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  • sirhk

Posted October 15, 2001 - 09:09 PM

#11

Did you see my newest reply to the other thread about this weekend. Maybe I'm a complete idiot but I don't see how you all are easily getting to your jets. I seriously think I would have to remove the carb which isn't the easiest task. It sounds like everyone else is just spinning their carbs in the boots to get access. Why won't mine do this. It hits everything it possilby could when I try to. Anyways, I think for this Sat. I'm just hoping you guys can show me how to get access to the damn things and figure out what I have in there as a starting point and then I should be able to take care of the rest myself in the future. Just need help the first time.

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Khris
"What's that?"
"It's a Yellow 99' YZ400!!"

  • Ron_in_SoCal

Posted October 15, 2001 - 12:35 PM

#12

Khris,

Ya gotta take the thing out of the bike man! Its not a big deal to do, I don't even take the tank off the thing because of my stupid radiator braces are a pain. The hardest part is the throttle cables, and that's easier if you remove the coil. Saturday sounds good. I will e-mail Kirk re the details and let you know.

Well, the clip position #4 is too lean. #5 might work at 5000 feet. Will be running #6 for 0 feet. Bog is still there, barely, but its no better or worse than before. Feels good at position #6 here at home (60 feet). Hard to tell just riding around pissing the neighbors off. Ya gotta love motorcycles to appreciate the beautiful sound this thing makes.

Stupid neighbors! Posted Image
(just kidding)


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N 33'41.156" W117'59.749"
HelmetCam Videos

  • sirhk

Posted October 15, 2001 - 01:00 PM

#13

Uhhh, I knew that. I swear everyone makes it sound like they are just spinning the carb in the boots. I'll try and pull it out one of these evenings if I can get home in time. I think that's my biggest problem. Are you able to flex teh rear boot enough to get ti out without removing the air box? You can get to the cables okay with the Clark tank?

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Khris
"What's that?"
"It's a Yellow 99' YZ400!!"

  • Mojo

Posted October 15, 2001 - 02:11 PM

#14

Sirhk, It's not that hard. Pull the cables off, unroute the drain tubes and pull back on the rear boot. I've had mine out so many times, I've stripped the phillips head screws on the boot clamps. Replaced them with allen head ones.

  • James_Dean

Posted October 15, 2001 - 07:45 PM

#15

Ron,

The Sudco people don't know about the EKN because it is a Yamaha ONLY part. However, it is identical to the EMN in size by shifting it 1 clip leaner. When John is using EKN#5 this is identical to EMN#6. By comparison the '01YZ426 uses EJP#4=EMN#5+1/2, so you're very close to that also.

If you're careful, maybe try giving the accel pump about 1/2 turn more out and see what it does for the bogging. The easiest access while on the bike is with a long screw driver from the LEFT side across and from below by the swingarm. When you're down low you can look upwards and see the BK mod screw. This is much easier than accessing it on the right side. First time I've mentioned this.

James

  • Ron_in_SoCal

Posted October 16, 2001 - 03:51 AM

#16

James,

That makes perfect sense. I love it when that happens. The EMN needle was an improvement, although I'm not too sure about the BK mod. I was checking out the accessibility of the newly installed screw. It's tight, but you can get to it as you described. I'll "screw" around with it and see if cleans up.

As it sits, the MAJ & PAJ are as they came from the factory. I'm not even sure what the sizes are. I have a PAJ screw(?) and several MAJ sizes in my cache of goodies. Should I bother to tinker with these jets also to emulate what brother John has going on?

Thanks for the input. You've been a major influence here and if it where not for you & Taffy doing extensive research in this department I would not even consider doing this. The thing ran bitchen two days ago, now I'm shooting for super bitchen!

  • James_Dean

Posted October 16, 2001 - 07:21 AM

#17

Ron,

I would suggest the #100 pilot air jet or 1 turn out on the replacement pilot air screw (equivalent setting). Beyond that, things start to get fuzzy and hard to be sure what is best. The last 10-20% gain gets much more difficult. I would focus on a few main jet sizes until satisfied and then just go roost on some hill climbs! Posted Image

James

  • John_in_Long_Beach

Posted October 16, 2001 - 07:53 AM

#18

Ron & James,

I just started reading this thread. Yes I ride at Glen Helen, sometimes up in silverwood.

Yes Ron I am going to try out the 175 main. The reason that I think this might work are two fold.

1) At 8,000 ft several weeks ago up in crab flats "Arrowhead" I noticed that the EKN#5 was a little too rich, but the bike started clearing up and running well, once I got things up to speed on some of the fire roads and started getting on the main. This led me to believe that maybe there might be more power to be had with a larger main at lower elevations. (Just right at 8,000ft, maybe too lean at 1,000ft?)

2) I also noticed once I went with the EKN#5, there was more power in the midrange and this power did not necessarily carry from the needle to the main. (Just a feeling).

So I will try the 175 main and let you know what I think.

As for the accelerator pump. I have mine set to about .3 seconds (just a rough guess) and I am thinking of increasing this a little.

What I noticed as I watched the squirt is that there are two levels of action. The first is that the squirt is powerful and strong. This seems to occur in the first .3 seconds, then the squirt kind of trails off but keeps going at about 1/3 the intensity and dripples out for the remaining 3 seconds about.

So I limited the squirt to the more intense beginning section.

As for the jetting changes. I don't remove the carb. From the left side of the bike loosen the back air cleaner boot, and push it behind the frame so that it is out the way. Then pull the carb out of the intake boot. For the needle rotate the top towards you. For the main and pilot rotate the bottom towards you. It is also a help to disconnect what I think is the throttle position sensor. No need to mess with the thottle cables. Very quick and efficient.

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2000WR - EKN#5, 172MJ, 226MAJ, MAJ Passage drilled to 278, 48PJ, 100PAJ, YZ timing, BK mod, 3/4 turn pilot screw, DSP tapered header and pipe, IMS tank & YZ seat, Scotts dampener & triple clamp & Renthal Fatbar 971, White Bros suspension, Dunlop 756's.

  • Ron_in_SoCal

Posted October 16, 2001 - 10:06 AM

#19

You know John, when you say "I also noticed once I went with the EKN#5, there was more power in the midrange and this power did not necessarily carry from the needle to the main. (Just a feeling)", believe it or not - I had the same feeling just blasting down my street. I did put a few hot laps in around the block to get that bugger up on the main and it felt like it flattened off a bit, whereas with the previous 180 main the thing really came alive at wfo.

I wonder, do ya think it's the exhaust system we are running that might be causing the thing to want a larger main than what James' extensive research would suggest?

Hummm, a 175 main and the needle clip at #3 or #4? Maybe I'll see if I can give this a try without completely removing the carby tonight. Besides, I need some practice getting at the carb so this is a great excuse. It's times like this that I'm glad the thing has a headlight.

Watch out neighbors, here I come (again)!

  • sirhk

Posted October 16, 2001 - 10:29 AM

#20

Hey Ron if I remember right the first post I saw from you had something about how hypocrtical it was for it to be okay for Harleys to cruise with loud exhaust but not Dirt Bikes. Is this some method of you trying to fit in on the street with the Hogs? Posted Image

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Khris
"What's that?"
"It's a Yellow 99' YZ400!!"




 
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