BK jetting question

27 replies to this topic
  • motoman393

Posted September 08, 2001 - 10:11 AM


I dont know if you know or not but, Mills Road MX has closed down and they are building a new track in Conroe. The old track the had was the best in Houston and I have heard the new track is WAY better than the old one. I will for sure be planning a trip out there. I ride at local tracks like: 290, Highlands, Rio Bravo, Super Daves, TX Motoplex, Mills Road, and I have been wanting to try out Longhorn MX in Beaumont (it is covered in!!)


I get my kicks on a 426!
Motoman393's MX Site

  • forloop

Posted September 08, 2001 - 02:03 PM


Rode RIO this morning. Dirt was great. Bike ran perfect. I did not notice any lean conditions. It screemed all the way to the rev limiter.

I am really curious about this 168 main jet. I don't understand way limiting the acelerator pump would affect the main jet. Once you get it WFO the pump does not come into play. Now, I can easily unserstand how it affect acceleration, but I don't see how it would affect a constant speed.

We need someone with a O2 sensor to check things out.

01 YZ426F #85 Vet C

  • motoman393

Posted September 08, 2001 - 03:35 PM



I also have an aftermarket pipe (WB R4) and im sure this needs more gas on the top end = larger main jet. Who knows...let me know where you are riding next weekend! Maybe we can hook up and ride! We havent been to Rio in awhile and Im sure it would be fun (you really get to open the YZ up out there lol) Later,


I get my kicks on a 426!
Motoman393's MX Site

  • G-Man

Posted September 08, 2001 - 05:46 PM


Ok I changed the main to the 168.

Pilot Stock
Needle Stock and position
Fuel Screw 1.75 out
Stock Pipe
1.5 gal AV Gas to 3.5 gal Pump.

Ran it down the street, 4th gear monster wheelies!!! Didn't seem to have quite the snap as yesterday, but I won't know for sure until the track tomorrow.

Did a plug chop, Plug was greyish.
Gonna try it tomorrow.

I'll let you know.

Moto to Live
Live to Moto


[This message has been edited by G-Man (edited September 08, 2001).]

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  • forloop

Posted September 08, 2001 - 06:41 PM



I have been riding Saturday mornings at RIO. I get there before 8:00 AM and ride until noon. Much cooler that way. I wish some of the other tracks opened early.

I am still wondering about that 168 main. Too bad we can't rig up an O2 sensor.

Did you notice any difference with the 168 in there?

01 YZ426F #85 Vet C

  • MX_Tuner

Posted September 09, 2001 - 03:10 AM


An O2 sensor wouldn't be hard to hook up if you had a donor head pipe. In fact, I may have a dented White Bros Ti head pipe that I can weld a nut to. I have the right size nut for a sensor to screw into and a good used sensor I believe.

Anyone have the time and desire to do some experimenting?

MX Tuner

  • Wyatt

Posted September 14, 2001 - 04:54 PM


What is the general opinion?? Is a white plug okay, or is it too lean??

  • mikeolichney

Posted September 17, 2001 - 04:05 PM


I thought the same thing about why the main is affected by this mod. After doing the mod this weekend, I understand why you want to go up on the main jet. The APJ is dumping fuel into the carb even at WOT, for 2 to 4 seconds after opening! You will see this as soon as you do the mod. So the main jet IS affected. I dont think I am ever WOT for much more than 4 seconds on our tracks. You need to compensate for the lost fuel, even at WOT.

I would think des racers who are WOT for more than 2-4 seconds would really like this mod, the bike would not go lean on them after the AP jet stops squirting fuel. Jeez, this must have screwed up some dyno readings...

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