Jetting q's after the BK mod...

4 replies to this topic
  • rwhitlock

Posted October 19, 2001 - 05:58 PM


Sorry to ask this, but I am rather new to the jetting world. I have read numerous posts about the Burger King (aka BK) mod an took the plunge and did it today. All went well, I had printed off several different posts and went with no problems. The squirt time is less than 1 second. The bike is an '01 WR 426

However, the snap on the bottom is gone! If I jump the throttle quick it will die. If I roll on, it goes ok. Once I hit about 1/3 throttle I can wick it and it will not die, just rev slowly.. No longer a quick hitter.

With that as my problem let me add the following info:

Main Jet - 165
Pilot Jet - 42
Main Air Jet - 200
Pilot Air Jet - 75

Pilot Air Screw - 1 3/4 turns out. (This is the screw directly under the intake in the center of the carb)

Needle - not sure. Don't have the right damn allen head wrench to get the top off. What ever came stock.

I have the stock exhaust with the plug removed. Air box lid off, YZ throttle stop. I live in Utah and the elevation is 4000 feet. I mainly ride mountain trails between 4500 to 6500 (max) elevation. The bike seemed to run fine before the mod. Since I ride trails mainly, I don't use 100% throttle all that often. Occasional hill climbs, but mostly low and mid range.

I have tried to make sense of the manual about lowering the clip, raising it, and am just confused as to which way makes it richer or leaner... Or do I need to work on the pilot jet?

So, if any of the jetting god's (and you know who you are.. :-) ) would like to point me in the right direction I would be grateful.

Thanks for your time, and I hope to have this baby back together soon!


[This message has been edited by rwhitlock (edited October 19, 2001).]

[This message has been edited by rwhitlock (edited October 19, 2001).]

  • rwhitlock

Posted October 20, 2001 - 09:14 PM


So far I have lowered the clip one position, and turned the air screw in 1/2 a turn.

This has made a good, noticeable difference. Do I continue with lowering the clip? Do I go with a bigger pilot jet?



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  • yzernie

Posted October 20, 2001 - 10:19 AM



I live in So. Cal. am also at about 4000'. I have been messing around with mine but I have a YZ not WR. Is your cam timing still WR??

I have found for me that a 45 pilot, one leaner on the needle, a 168 main and 1 out on the fuel screw is working great for me. One difference would be your timing and I don't know how much that by itself affects the jetting. I don't think that would cause that big of an issue. I also run race gas which will make my jetting a bit leaner.

If you run pump gas, I would suggest a 45-48 pilot, stock needle setting, a 170-172 main and one turn out on the fuel screw.

The needle, if you raise the clip position on the needle you will lean the needle. If you lower the clip position on the needle you will richen the needle. Alot of people use different terminology when talking about needle positions. When in doubt, ask!!

Hope this helps you, Ernie

--Life is too short, work hard--
Sponsored by Yamaha of Cucamonga, Larry Roeseler's Stroker Fourstroke Speed Equipment and Answer Racing,

  • James_Dean

Posted October 20, 2001 - 12:29 PM


The usual plan with the reduced accel pump flow is to richen the needle by lowering the clip position 1 step. You should also consider one of the YZ carb needles. Look for discussions about EKN, ELN etc.


  • MN_Kevin

Posted October 20, 2001 - 12:31 PM


Just to let you guys know (as Ernie accurately wrote), the screw under the carb is a FUEL screw. The more you turn it out, the more fuel passes through.

The pilot air screw (PAS) is an AFTERMARKET part purchased through Sudco. If you remove the intake bell (or whatever it is called) that mounts onto the carb venturi adjacent to the airbox, you will see two jets. These are the pilot air jet and main air jet. Switching to a pilot air screw w/ spring allows for raising or lowering pilot air flow.

Just and FYI...


'99 WZ/YR (you choose!) with ALL YZ mods, de-octopused, DSP Doug Henry airbox w/ velocity stack, FMF PowerBomb header, Stroker SX-1 silencer, SS front brake line, OEM YZ tank, IMS YZ seat, Mobil 1 15W-50.


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