YZ426 carb needle

What size needle is stock for a 2001 YZ426? Mine has the OBEKR and I am struggling with jetting, unable to eliminate the off idle bog. Tried everything between 40-48 pilot, all needle clip settings on the OBEKR, 160-172 main, and have done the BK mod. I just rebuilt the motor top to bottom, starts easy and runs strong but will die with a quick stab on the throttle, whether its on the stand or on the road. It seems a different needle is the only thing left to try.

Stock on a 2001 is an OBEJP, clip in #4.  There are two differences between that and the OBEKR, the taper, and the diameter of the upper straight portion, this last of which is a major influence on the response of the engine when transitioning from the idle circuit to the main.  The EKR is larger on top, and thus leaner, so that can be a part of what's causing the stumble. 


Also a possibility is the accelerator pump performance.  Pump timing is adjustable, and needs to be set just late enough that the stream of gas does not strike the slide as it opens.


The OBEKR was standard on a 2000.  The number on the left side of a 200 carb should be 5JG1 00, whereas a 2001 model should be 5JG5 50.  The carb could well have been swapped early on.


Look in the Common Threads pinned topic.  There are links in those two posts regarding:


Free downloads of service manuals


The BK Mod for 426 accelerator pumps.


Jetting, etc.


This from the '01 manual:






Ok Gray, thanks for the info, the carb is infact the 5JG1, so it is off a 2000. Is there anything else different between the 2 besides the needle? I did already try the BK mod, went from a 3-4 sec spray to about .5 sec and had it timed so it just cleared the slide. It actually seemed to make the problem worse. Leads me to believe that I was already too lean, and lessening the spray just compounded the problem

Edited by alping45

Here's the carb info from the 2000 manual:




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