put the 01' needle and 03' AP diaphram in my 00'. It lost its hit

I got the 01' OBEJP needle and the 03' optional AP diaphram for my 00' 426. I put the needle in the 3rd position and everything else is stock.

I went riding yesterday at 3500 ft temp around 70-75F and the bike still has a slight bog off idle :) and seemed to have lost some of the hit it had before.

Its not slower, it feels much smoother and doesn't rev as quickly. The top end pull feels stronger now too.

Is that what the OBEJP needle should do?

I've heard that the 01' needle was a must have, but never heard why its a must have.

Any other ideas about this damn bog? The 03' diaphram was supposed to cure it but didn't.


The 01 needle is supposed to help with the bog as well. Put your stock AP diaphragm back in and see what happens. Have you done any other carb mods (GB mod/JamesNow)?

Try the needle clip in the fourth position from the top, stock on the '01. You will also need to check the AP circuit timing and duration and adjust it accordingly using the BK mod...162 is the stock main jet and 42 works best for the pilot jet. Is that what you're running?

As far as I know the jetting is stock. I only replaced the needle (3rd pos.) and the diaphram.

I'll try putting the needle back in the 4th pos. and see what happens.

My biggest thing is what should I have expected from the 01' needle?

The bike runs good with it, the midrange hit has kinda weakened but the top end pull is killer now. Is that what the OBEJP needle should do?

Also, the 03' AP diaphram should resolve the issue of the wrong squirt duration. I was speaking to JD on the jetting forum and he advised this will do the same as the BK mod (which I did not do).

I'm going to get a few more rides in with the JP needle and switch back to the stocker and see which I like better. I may not miss the hit as much as I think I will.

Thanks again.

The stock '01 position (4th clip) would be too rich for that altitude on my bike (stock '01). Not only would I recommend the 3rd clip, but I would go as far as suggesting the 2nd clip.

Make sure you have about a 162 main. A 158 wouldn't be out of line for your elevation as well.

I would also possibly recommend a 40 pilot. A 42 is probably too rich at that elevation.

Thanks for the input.

Does anyone know what stock jetting on a 2000 YZ426 is?

I dont see any mention of it in the manual.

I initialy did the '01 needle swap, but after I 'got into' my carb I ended up with the stock needle and a pilot jet one size down. As far as the '03 AP Diaphragm, I went with a P-38 Ligthning, that, and a Storm idle jet (finger knob type) and all the bog is gone, nothing but snap :D. Good for sea level to about 7500 feet! Oh yeah, and a Free PowerNow! :)


what did you first experience with the 01 needle and how come you went back to the stocker?

What is the P-38 Lightning (sounds like a fighter plane)?

And what does the Storm idle jet do, I never heard of it.


Thanks for the input.

Does anyone know what stock jetting on a 2000 YZ426 is?

I dont see any mention of it in the manual.

162 main, 42 pilot, 1-1/2 turns out on the fuel screw.

Thanks Cowboy.

I'm gonna try a 158 main and 40 pilot and see where that gets me. According to the jetting guide on Motoman's site I should be running a #40 PJ, needle at #3 pos., #158 main and 1.5 turns out on the fuel screw for my altitude and temp.

You guys we're right on with your recomdations for the main and pilot. Good one! :)

YOu can always find the stock specs on the Yamaha-motor.com website for the jets. Look under the part microfiche.

This is the stock specs listed on the Dealer service site:


Manufacturer / Type KEIHIN / FCR39H

ID Number 5JG1 00

Main Jet / Pilot Jet #162 / #42

Pilot Screw (Turns Out) Æ

Needle Jet / Jet Needle Æ / OBEKR

Clip Position / Slide Cutaway 4 / 15

Float Height 8mm (0.31in)

Fuel Level Æ

Idle RPM 1700~1900rpm

Set CO% 4~6%

Basically if you lost the hit, usually says you are to rich. No suprise with that overly aggressive AP circuit. I did not go the same route you did, I went with the BK mod and JD jet kit. Worked out perfectly for me at 1.25 turns out on the fuel screw. You may want to try that, be sure to get a zipty fuel screw or similar.

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