BK jetting question


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

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).]


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

Hey guys,

I just did I plug check on my bike. It was a little on the lean side (half white/half wheat bread brown= just a little lean). I replaced the 162 main I had with a 168 and Im sure this will help my readings. I also double checked my fuel screw and re-set it back to 1 3/4 turns out (42 pilot) somehow all the track adjusting it ended up at 1.5 turns out! My bike runs best with the needle setting at stock middle position. I will let you know how it runs whenever I ride it! Later,



I get my kicks on a 426!

Motoman393's MX Site

I still run the stock pilot (42) and the fuel screw about 1 3/4 out.

Sounds like several of us could get together and do some roosting. I hear a new AMA sanctioned MX park is being constucted in Conroe in the very near future.

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

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

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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