Leak Jet on a 426 Question


7 replies to this topic
  • YamahaDoc

Posted April 07, 2011 - 02:56 PM

#1

Ok I was wondering if a leak jet will solve my issue... I posted this in the Jetting section but haven't got any replies yet. I figured Id you fellas:

Here is the good stuff.


2002 Yamaha YZ426f

2200'/70*/No Humidity Issues ~40% All year/Desert, Dunes, Trails

HMF Competition Stage 2 (flows a little more air then stock)/ No air box lid, With No Toil filter W backfire screen/ nothing to the motor Ive done the " O Ring Mod"

Current Jetting:

Main: 162 (stock)

Pilot: 42 (stock)

Starter: I think 72 but that shouldnt be my problem, it starts like a dream.

Needle: OBEJP 4th clip

Issue: I just have bog in the low. Rolling in 2nd gear to full throttle immediate bog then clears up when the fuel burns off, Happens everytime all the time. Im new to 450's so I dont know what to change first! I can do all adjustments and change jets that no big deal I just dont know anyone that has alot of knowledge on these bikes!

Motor is 100% sound valves checked perfect, im positive of all that.

Im wondering if the addition of a leak jet might be the solution?

Thanks Guys!

  • grayracer513

Posted April 07, 2011 - 03:21 PM

#2

Most of the time, this works on the 426:

http://motoman393.th.../tech/carb.html

  • YamahaDoc

Posted April 07, 2011 - 03:41 PM

#3

Most of the time, this works on the 426:

http://motoman393.th.../tech/carb.html


Thanks!

I was hoping to here your answer! I saw that on the "sticky", so does this just help to time the AP? Or does it shorten the length of squirt? Mine starts as soon as the throttle starts rolling on :/

I also read somewhere that leaning out the stock needle one clip could help? any truth to this? And if so do I need to adjust anything else IE jet size??

  • grayracer513

Posted April 07, 2011 - 06:43 PM

#4

The taper of the needle does not lift above the discharge nozzle until about 1/4 throttle, so raising/lowering it has little effect on anything that comes before that, but above that point, lowering may help. Alternate needles with a larger diameter on the upper, straight section can be used to lean the mix between 1/8-1/4.

The BK mod is mostly about shortening the duration of the squirt, so the pump timing also needs to be looked at. Review the manual for the procedure.

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  • YamahaDoc

Posted April 07, 2011 - 08:58 PM

#5

The taper of the needle does not lift above the discharge nozzle until about 1/4 throttle, so raising/lowering it has little effect on anything that comes before that, but above that point, lowering may help. Alternate needles with a larger diameter on the upper, straight section can be used to lean the mix between 1/8-1/4.

The BK mod is mostly about shortening the duration of the squirt, so the pump timing also needs to be looked at. Review the manual for the procedure.


Thank You so much!

  • Chas_M

Posted April 08, 2011 - 06:31 AM

#6

To adjust and shorten the squirt duration on my FCR carbs, rather than doing the complete BK drill and tap mod, I simply Super Glue an appropriately size small nut to the 'BK AP tab' to limit the AP pump throw.

  • YamahaDoc

Posted April 08, 2011 - 08:41 AM

#7

To adjust and shorten the squirt duration on my FCR carbs, rather than doing the complete BK drill and tap mod, I simply Super Glue an appropriately size small nut to the 'BK AP tab' to limit the AP pump throw.


That sounds like a good idea! Do you know what size nut you have, just for a starting place?

  • Chas_M

Posted April 08, 2011 - 11:07 AM

#8

That sounds like a good idea! Do you know what size nut you have, just for a starting place?


I don't recall offhand, but it needs to be around 1/8" or 3+mm thick or just enough to limit the squirt to 1 second or less.





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