Question about fine tune jetting 426 any suggestion?

7 replies to this topic
  • motoxgp

Posted June 24, 2010 - 05:28 PM


2002 WR426 supermoto.

I did the YZ timing, uncorked pipe and air box, and bk mod to about .4 sec or so.

gray wire also.

I have a 172 main, and 45 pilot

The stock needle is raised one from the middle

the fuel screw is 2.5 turns

the bike runs good, but here is the issue.

from idle, if I twist the throttle super super fast it bogs and will die.

This only happens if I twist it super fast (fastest possible, like a reflex)

If I am at 1/8 throttle and hit it, its fine, just a little bog,

How can i get rid of this?

do I need different jets or needle, or do I need a more powerful squirt from the ac pump.

  • grrrr

Posted June 26, 2010 - 12:58 PM


I just did my 450. Ised a Jt jetting kit. It came with the ac pump stuff, works fine.

  • GCannon

Posted June 28, 2010 - 09:35 AM


Try backing off the BK screw a little and getting a squirt time around .6-.75 seconds duration. You may not have enough fuel in your squirt volume to cover the giant vacuum leak you created when you quickly opened the throttle. Your Main Jet seems rich are you at sea level?

  • co-rydr

Posted June 29, 2010 - 03:29 AM


Hi, Is there a way to measure at the BK screw that would let you know the fuel duration. I thought that I read it on TT a while back. I was not trying to hi-jack, just thought it could be helpful if someone knew. Thanks

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  • Kawidad

Posted June 29, 2010 - 07:14 AM


You might try a 48 pilot and backing off of the idle screw. You might have too lean a pilot jet and are compensating with a rich idle setting.

  • Pooley

Posted June 30, 2010 - 06:29 PM


Forget the BK mod. Do the O-ring mod, it is WAAAAAAAYYYYY better and will immediately fix your low end bog.

  • motoxgp

Posted July 02, 2010 - 01:30 PM


I am at sea level. No way on the 48 pilot. The best way to know if you are too lean on a pilot is to engne brake pretty good and see if your motor pops. If it does you are too lean.

I think I will back off the bk mod a bit, even though it had this problem before I did the mode

  • byggd

Posted July 02, 2010 - 02:22 PM


The stock needle is raised one from the middle

Did you raise the clip one notch (lower the needle) or lower it "raising" the needle?


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