BK Mod and Dubach Pipe

bassr #186,

Add the pipe first, then determine if you need the BK mod. I have an `01 and the DRD pipe and I don't have the "bog" problem. As far as jetting, you should go a little richer, though last summer, I had stock jetting and lowered the clip(for other reasons)and the bike ran super. When it started getting into the colder months, I really had to experiment w/the jetting to overcome the cold starting problems.

Hey Bassr

I live in Houston and ride 290,Rio, Mudoplex, Highlands etc. I am running a 2000 426. I do have the BK mod done. I have Dubach pipe and a twin air filter. The jetting I run, Pilot jet is a 48, Main Jet is a 170, needle is a OBEKR (stock) clip in 4th groove down. It runs so hard it yanks your arms off. I do notice a difference between Uni and twin air filters. Twin air seems to flow better. Cya and good luck

O yeah I have the pilot screw out 1&1/2 turns +/- a 1/4. Pump squirt on BK Mod is approx 1/3 of a second. Hope it helps.

I am about to do the BK mod and add a Dubach pipe to my '00 426. If you are running this set-up, what jetting specs, clip position, etc. are you running? The altitude here is about 100 foot above sea-level and it will soon be hotter than Hades. Thanks in advance.

Hey Bro I have the DR.D pipe on my 00' and trust me you'll still need the BK mod. I'm planning on doing the BK to mine here in a couple of weeks. I stalled out and lost at least three positions at my last race and I'm going to put in the BK so that'll never happen again.

Thanks for the replies. I am ready to get rid of the bog. To keep from accidentally killing the bike out of a corner, I have to run the idle pretty high right now, which sometimes makes the transition out of tight corners pretty tough.

Fastest1 - we should get together and ride sometime. I primarily practice at 3-Palms and Splendora because they are closest to Tomball, but I hit the other tracks before a STC series starts.


The needle Yamaha delivered in the '00 YZF is hopelessly lean on the straight diameter. The best twelve dollars you can spend on your bike is to buy a stock/standard (or whatever) needle from an '01 or '02 YZF 426.

The stock '00 needle is an OBEKR

The stock '01/'02 needle is an OBEJP

So the latter is one half clip richer (K to J) and two sizes richer on the straight (R to P), which governs lower throttle settings and kind of crosses over with the pilot size. This will probably do as much to help your throttle response off idle as the BK mod.

Finally, I have to include the following rant:

IMO the stock YZ pipe vs. every aftermarket pipe I've seen (except the FMF Q) is, generally speaking, a wash jetting-wise. Changing pipes on an already unrestricted thumper is not like changing pipes on a two stroke. The best analogy you can make is that changing a two stroke's pipe is like changing the cam(s) on a thumper.


At your elevation you may prefer a clip position richer, maybe not (remember the ’01 needle is effectively a half clip richer already). You also may benefit from a richer pilot. I would guess a good starting point would be:

Stock '01 YZ needle (EJP) on 4th clip (stock ‘01/’02 settings)

45 pilot

Go ahead and try a larger main, but this makes less difference.

Another popular trick around here is, once you have arrived at a good main jet size, try a few mid to high rpm, open-throttle passes with your Main Air Jet removed. A lot of guys get better/crisper overrev with the slightly increased flow you get by removing this air jet altogether.

Finally, if, once you have all your jetting set, you are experiencing an obnoxious amount of popping on decel with your aftermarket pipe, the best cure is to go progressively smaller on the Pilot Air Jet. You can buy and adjustable one from Sudco or Carb Parts Warehouse for about $14. The PAJ governs mixture in concert with the Pilot Jet at higher rpms/lower throttle (more or less). Sure, you can cure the popping by going richer on pilot and idle mix, but in my experience by the time you get things quieted down your throttle response suffers from an overly rich idle/pilot.

Hope this helps.

[ May 10, 2002: Message edited by: Hick ]

Oops, double post :)

While I'm here let me add that almost anybody with an '00 YZF 426, especially at lower elevations, will probably prefer the '01 needle.


[ May 10, 2002: Message edited by: Hick ]


I would love to go for a ride. We just had a boy 2 weeks ago so I think I am out of the circle for a while. I am trying to earn bonus points by sucking up so she will let me soon. With 2 screamers around she is reluctant to let me get out just yet. Keep checking here on thumpertalk and we will meet up and ride. Cya & Good Luck with the jetting keep us informed of the results. :)

Hick: thanks for all the information. I never knew about the differences in the needles. I am tempted to swap the needles first so I can see what impact that has by itself.

Fastest1: keep the faith, you'll be back on the track soon. Change enough diapers and you will earn the right to ride again. Let me know when you are ready to go.

[ May 13, 2002: Message edited by: bassr #186 ]

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