WR426 Jetting Help

Folks...wondering if anyone can help with a jetting question.

'02 WR 426, just installed JD Jet Kit (170 main, blue needle on 3rd clip, 42 pilot).

First...I am getting a very distinct miss at 1/8th throttle that clears up just past 1/8. This was not a problem prior to JD kit. Also, I am getting no response from the Fuel Mixture Screw.

Minor mods: exhaust Hot Cam, 'normal' WR mods.

Any thoughts?

Did you have the slide out?

Same pilot as before the JD kit? If so, the kit would not affect things.

Yes...factory 42 pilot; no on the slide, just changed the needles.

Very distinct miss as I just crack the throttle, pulls clean beyond that point.

I had to drop to a 38 PJ when the JD kit was installed but this sounds more like a change in the needle height is needed. Did you have the pilot needle out when installing the JD kit? If so did you make sure the o-ring and washer weren’t misplaced?

No, I did not pull the pilot during the installation...but did pull it after I noticed the 'dead spot' and blew it out to be sure.

As for the needle...up or down? I am using the blue needle at 500ft, temp was approx. 75 today.

I could be wrong but I sounds like a lean miss to me so the needle would need to go up (meaning clip down one notch). A move to a 38 PJ might have the same results. Is the bike running hot?

No...the bike runs fine other than the miss. Moving needle to 4th clip, that was the stock setting as well...as if that means anything.

Thanks for the help...4th clip definately cleaned up the dead spot. Will run it tomorrow to check entire throttle range again.

Question...is the 'red' needle strictly a high alt / hot needle or is it for either / or. If so, at what temp does the 'red' come into play?

Thanks for the help...4th clip definately cleaned up the dead spot. Will run it tomorrow to check entire throttle range again.

Question...is the 'red' needle strictly a high alt / hot needle or is it for either / or. If so, at what temp does the 'red' come into play?

Always glad to help! I’m not sure what the use of the red needle is but I think you are correct that it’s used for hot areas. I run the same setting from 800’ to 5000’ and my 02 runs awesome!

I had to drop to a 38 PJ when the JD kit was installed but this sounds more like a change in the needle height is needed. Did you have the pilot needle out when installing the JD kit? If so did you make sure the o-ring and washer weren’t misplaced?

I think what byggd meant by "pilot needle" was actually the pilot circuit adjustment screw. If the o-ring and/ or the washer were missing then your could have these symtoms (lean). Did you include the o-ring mod to the AP linkage?

Red is for high humidity as well.

I think what byggd meant by "pilot needle" was actually the pilot circuit adjustment screw. If the o-ring and/ or the washer were missing then your could have these symtoms (lean). Did you include the o-ring mod to the AP linkage?

Yeah sorry. I should have said "fuel mixture screw"

http://shop.thumpertalk.com/product_p/fms01.htm

After dropping the needle clip, I found the 'dead' spot still remains when I blip the throttle, not as pronounced when I gradually advance the throttle.

OK when cold, 'dead' spot as I blip the throttle after a hard run and hot. Could the pilot circuit be too rich? 42 pilot...cool weather today.

Thanks

Here is my current jetting etc. It has a flat spot when cold but it goes away after the motor reaches 100 degrees.

Model (400 - 426 - 450): 02 WR426

Timing (WR-YZ): YZ with 03 exhaust cam

Main jet: 170

Pilot Jet: 38

Fuel screw (turns out): 1 1/2

Needle model/Clip position: JD blue needle position #3

Airbox lid (on or off): Lid Off

Pipe: Stock exhaust with peashooter removed

Altitude where you ride: So Cal 600-5000 ft

Temperature where you ride: 40-100

Okay...will share my solution for anyone in future need.

Trial and error...I found that the AP was hitting a little too early, 'retarded' the squirt with a 1/2 turn in, cleared up the problem in short order. Still not sure what caused the change??

And just a side note...James Dean returned a call after hours to answer questions regarding the problem after my JD Jet install. Very knowledgable guy and great after purchase support. Cant say enough about his service!

In some cases, jetting in one area 'compensates' for shortcomings in another. You were probably a little rich in the straight diameter of your old needle, so the missed squirt was compensated by the slightly rich needle. When the JD needle leaned things slightly, that compensation was gone, hence the faint bog.

This is one of the reasons that basic jetting must be correct, then left alone when curing a bog. You do not want to be chasing your tail. Always make sure the basic, irrefutable settings are right.

Correct poilt and fuel screw setting, set for idle them LEAVE ALONE.

Correct Main jet for WOT, then LEAVE AlONE

Correct needle and clip position for stead state, constant throttle operation, then LEAVE ALONE

Set AP Timing, the LEAVE ALONE

Select leak jet

I'm glad you got your JD kit to work:thumbsup: Mine is on the shelf, Fortunately i was able to get mine running great with Yamaha parts. Ride on:ride:

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