BK jetting question

For the 01 owners who did the BK mod

1) Anyone do the mod like me, no jet changes (fuel screw 1.75), and notice a difference on the track?

2) Anyone change the jetting AFTER the BK mod, ad notice a significant change. BK said "if you don't change the jet to a 168 your only doing HALF of the mod".

He was running a DSP titanium pipe, I have the stocker.

Question is do I STILL need to change jetting to get the TRUE performance of the mod? Mine is bone stock, and ran perfect in the street yesterday. Would putting a richer main jet foul things up?

3) I have not done a plug check yet (pain in the ass) on these bikes do you do a WFO plug chop like on a 2-smoke?

Thanks,

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Moto to Live

Live to Moto

http://www.geocities.com/gmann_3000/

G-Man

G-Man,

I have done the Mod for three differen't folks now and all have been impressed. The bike does seem to be sensitivite to Temperature changes more so than in stock trim. For my area, the 45 pilot, 1 clip richer on the needle and a 165 main seems to work well, however, as it gets cooler, I may go back to the 168 main.

[This message has been edited by MrMXer (edited September 07, 2001).]

Did u try it before a jet change, or did u change the clip position at the same time?

2) Anyone change the jetting AFTER the BK mod, ad notice a significant change. BK said "if you don't change the jet to a 168 your only doing HALF of the mod".

He was running a DSP titanium pipe, I have the stocker.

Question is do I STILL need to change jetting to get the TRUE performance of the mod? Mine is bone stock, and ran perfect in the street yesterday. Would putting a richer main jet foul things up?

Motoman has mentioned that the BK mod cannot be used on the older models (i.e. 99' yz400)Why not? Thanks

I did a bunch of practice starts yesterday. I run stock pilot, thrid clip and a 158 main jet with 50/50 race gas.

I did not notice any lean spots. Take that back my idle hung a tad when I reved it. I will add a touch on the fuel screw.

I have my duration set to .5 seconds and the delay is adjusted for best throttle repsonse. I have not checked were the squirt is in relation to the slide.

It's a hole-shot machine. I think I am going to remove the front wheel. I don't have a lot of use for it now.

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Rick

01 YZ426F #85 Vet C

Jetting is rider specific...some people prefer richer jetting and others like it on the lean side! You just have to ride the bike and make adjustments as you go (it is real easy to swap jets at the track) There is no "magic setting" for your jetting...I wish there was! So just try a few different jets. I recommend going richer first (cause too lean can burn your valves up) and whenever your bike begins to feel sluggish (if that is possible on a 426cc bike LOL) lean it out a tad! I am gonna put a 168 in mine soon because my top end is a little flat (and I always ride the rev limiter) Hope this helps,

Garrett

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I get my kicks on a 426!

Motoman393's MX Site

Originally posted by motoman393:

Jetting is rider specific...some people prefer richer jetting and others like it on the lean side! You just have to ride the bike and make adjustments as you go (it is real easy to swap jets at the track) There is no "magic setting" for your jetting...I wish there was! So just try a few different jets. I recommend going richer first (cause too lean can burn your valves up) and whenever your bike begins to feel sluggish (if that is possible on a 426cc bike LOL) lean it out a tad! I am gonna put a 168 in mine soon because my top end is a little flat (and I always ride the rev limiter) Hope this helps,

Garrett

Originally posted by motoman393:

Jetting is rider specific...some people prefer richer jetting and others like it on the lean side! You just have to ride the bike and make adjustments as you go (it is real easy to swap jets at the track) There is no "magic setting" for your jetting...I wish there was! So just try a few different jets. I recommend going richer first (cause too lean can burn your valves up) and whenever your bike begins to feel sluggish (if that is possible on a 426cc bike LOL) lean it out a tad! I am gonna put a 168 in mine soon because my top end is a little flat (and I always ride the rev limiter) Hope this helps,

Garrett

Garrett,

Did you do anything with your needle position.

BK said "lift the needle one clip position". Does this mean lowering the clip which would "lift the needle" making it richer?

I'm gonna go ahead and put the 168 also to be on the safe side.

Thanks,

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Moto to Live

Live to Moto

http://www.geocities.com/gmann_3000/

G-Man

No, my needle is stock position (in the middle) You are right about the needle clip... lower the clip to make it richer! Let us know how you like it and how your jetting works!

Garrett

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I get my kicks on a 426!

Motoman393's MX Site

[This message has been edited by motoman393 (edited September 07, 2001).]

This is too cool!! I wonder if Yamaha has seen the Carb. Mod yet? I hope BK didn't piss anyone off by this post!!!!

Jetting ?'s

If your jetting is stock after the BK Mod you do have to jet for your application. Woods/MX ..And the Specs that are for Timmy's bike ----(this is a top 5 guy now ya know!)My bike may not go as fast as his on a regular basis(get the point?)So Brian's jetting may not suit everyone or anyone at our level!!!

Nah...I think Yamaha designed the carb to allow the accel. pump adjustment screw. They didnt have to put the tab on the side of the carb (to allow us to drill and tap a hole) and they didnt have to notch out a circle on the black dust cover either! Yamaha is smart, they knew what they were doing when they designed the carb...but they arent going to advertise "hey all you 426 owners get free HP with the BK mod...come and loop out your brand new YZ with this neck snapping acceleration modification" LOL They put it there so the "advanced" rider could tinker with their bike and squeeze performance out of it!

I'm sure Yamaha R&D read this board...and I know Brian Kinney does (whether or not he replys is a ? ) Now that the nationals are over and it is the "break" maybe BK will come and hang out in TTalk again like he used to! Thanks,

Garrett

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I get my kicks on a 426!

Motoman393's MX Site

Before I performed the mod, I ran stock jetting and had sooty plugs. I performed the mod and the bike ran better than before, but plug readings showed a lean condition. (bright white color)

I swithced 1 step fatter on my needle position, but this caused what felt like a rich condition at intermediate cruising speeds.

I moved the needle back to stock position and switched to a 168 main. I could imediately feel a performance gain. The motor runs very crisp and pulls harder than ever with a full twist of the throttle.

But, plug readings (which are a pain in the ***) still show a lean condition. I will switch a step bigger on the main and do more testing to see if I can turn the plug brown.

I will post the results of what happens. I am going out of town for a week so it will probably not be until next weekend.

I encourage all of you that have done the mod to take a good plug reading. If you're like me, my bike ran so well after the mod that I never would have known that it was running so lean if I had not taken the time to read the plug.

2-4 seconds down to .3 seconds. That's a big difference and it could create a lean situation. Wouldn't want to damage anything!

"2-4 seconds down to .3 seconds. That's a big difference and it could create a lean situation. Wouldn't want to damage anything!"

Very good point, I kinda wondered about this myself, looks like I'm gonna put in the richer main (168) and raise the needle.

G-Man

I did the mod last night but didnt get a chance to start the bike and fool with carb settings. Im in the same boat as G,..engine (carb) is stock and Im also wondering if I'll need to re-jet..Also, what is the stock jet for an 01'? I did recieve another jet when I purchased the bike new, but I never looked at the size of that one either. Next project will be changing the fork oil...get ready for the questions! Thanks for the help.

Mike

I've enjoyed following the BK mod posts, sounds great and I should be doing the mod in the next few weeks. As far as stock jetting for the 01'. 42pilot/162main..my bike came with a 158/168mains also. I had the cold fouls this winter and Brian advised me doing the mod will cure this. Blipping the throttle while warming the bike was dumping waaay too much fuel in. I look forward to the crisp response all of you guys seem to be getting.

Hey Wyatt,

I saw you live in Conroe...I live in Friendswood and there are others who live in the Houston/Beaumont area in here as well! We all need to get together and ride!

What pilot jet do you have in your bike? And what is your fuel screw set at? Thanks,

Garrett

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I get my kicks on a 426!

Motoman393's MX Site

I have also done the plug readings and also have the whitish looking lean reading.I remember reading that a four stroke will not give a true "tan reading" .I'm running a 165 mj and it was a big difference from the stock 162 ,I may try the 168 and see if that will help the whitish plug readings a bit.I'm still getting a bit of carbon at the end of the exhaust,haven't really track tested the mod yet though.I believe I read the white plug =4-stroke thing at Dirt Rider .Net, Rich I think...

I dont know if you know or not but, Mills Road MX has closed down and they are building a new track in Conroe. The old track the had was the best in Houston and I have heard the new track is WAY better than the old one. I will for sure be planning a trip out there. I ride at local tracks like: 290, Highlands, Rio Bravo, Super Daves, TX Motoplex, Mills Road, and I have been wanting to try out Longhorn MX in Beaumont (it is covered in!!)

Garrett

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I get my kicks on a 426!

Motoman393's MX Site

Rode RIO this morning. Dirt was great. Bike ran perfect. I did not notice any lean conditions. It screemed all the way to the rev limiter.

I am really curious about this 168 main jet. I don't understand way limiting the acelerator pump would affect the main jet. Once you get it WFO the pump does not come into play. Now, I can easily unserstand how it affect acceleration, but I don't see how it would affect a constant speed.

We need someone with a O2 sensor to check things out.

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Rick

01 YZ426F #85 Vet C

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