HEADS UP!!!

Site upgrade in progress... Core site functions are working, but some non-critical features/functions will be temporarily unavailable while we work to restore them over the next couple of weeks.

Please post any bugs you encounter, but before you do, check to see if it's already listed.

Thanks for your patience while we work to improve the community.

Sign in to follow this  
Followers 0
YamahaDoc

Leak Jet on a 426 Question

8 posts in this topic

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!

Share this post


Link to post
Share on other sites
Most of the time, this works on the 426:

http://motoman393.thumpertalk.com/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??

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites
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!

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites
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?

Share this post


Link to post
Share on other sites
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.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now
Sign in to follow this  
Followers 0