Thunder Aley/BK mod

10 replies to this topic
  • pwisz

Posted March 17, 2002 - 05:40 PM


My buddy and I just finished the bk mod on '01 426's. Pretty easy. Now just waiting for my Thunder Alley pipe and was wondering what jetting changes to go with. Already went from 162 main to 168 and am wondering what needle setting to go with. Got it set in the middle(stock for here) but what should I be going with (@3200')??? Still snow on the ground and can't wait to try things out. Thanks for the help.

  • Shawn_Mc

Posted March 18, 2002 - 09:01 AM


Stay with the 168 main. I raised my needle 1 notch, and went to a 45 pilot. Man its fast. You might want to check out the blue wire mod listed in a different thread.

  • Greg

Posted March 18, 2002 - 02:14 PM


pwisz; What part of Canada are you from? I also just did a BK mod but haven't changed my jetting yet. Did you go to the 168 before the BK mod or after? Given the altitude in Calgary, I thought I would start with the 162.

  • h_bomb

Posted March 18, 2002 - 03:05 PM


Im running the same as Shawn Mc that seems to be the setup for our area,I also cut the light blue wire that goes to the carb.My bike pulls like John Forces funny car. :)

  • pwisz

Posted March 19, 2002 - 03:36 PM


Greg, Calgary as well and I went with the 168 just off the reccomendations from Bob Murray(Thunder Alley). I'm just trying to get her close for spring, can't wait till this snow leaves, unless you've had other experiences.

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  • Greg

Posted March 20, 2002 - 12:34 PM


pwisz; I cannot speak for the effects of the pipe on your jetting, but I thought given our altitude(3500ft) and our relatively lower temperatures to southern states that at #162 we were already a little on the rich side and with the BK mod it may put us where we want to be. I haven't tested the mod yet, it's just a guess.

  • Shawn_Mc

Posted March 20, 2002 - 12:51 PM


Lower ambient temps will require bigger jets. Altitude (up) requires less jet. So Yall got yer hands full

  • pwisz

Posted March 20, 2002 - 02:31 PM


Since I've already got her setup w/ the 168 and needle raised one, I'll probably leave it be. Trial and error I guess. Shawn, why did you go with the 45 pilot and what should I be looking for to decide if I am to go that route. I'm pretty green on this jetting thing. I was kinda thinking that with a 168, more fuel means more power. I really meant the green thing. I appreciate the help guys. Where do you do your riding Greg?

  • Greg

Posted March 21, 2002 - 06:22 AM


I am also new to the jetting thing. Can ya tell?
Shawn, I got my info from the manual and it appears to characterize high altitude and low temps simularily.
pwisz, I ride primarily at Blackfoot. On occasion I will ride at Waiprous Creek.

  • jamracing

Posted March 21, 2002 - 10:29 PM


I cleaned the midrange allot by using the stock YZ250f needle. Also, by putting in the BK mod, you'll have to fatten your pilot circuit (I went from 45 to 48). My jetting makes the motor electric-like, no coughs/sputters/burbles etc... Hell, it was good enough the holeshot the class at the GNCC! :)

  • John_Lorenz

Posted March 21, 2002 - 10:40 PM


I have made some minor changes in jetting including the BK. I have a stock 00, with the Wright Bros R4 and Header. The BK did one heckof alot for Bottom end and reving through the ranges, But when I started the Jetting portion it really made the differance in the BK and Pipe. I ended with a 45 Pilot, One Notch up on the Needle and a 168 on the main.

Also note that depending on the day Hot Cold and so on I will drop to a 165 main and place the needle back to standard.

Jetting is not OK Stop there on these bikes (SNOT A XR OR KLX) oil and gas lets go. These are race bikes and depending on Altitude Day conditions Temp and so on you may need to go up and down. Well at least I do, I like to run the bike at peak performance. I keep a chart of the Days I ride Temp, Wet Dry Hot Cold days and what Jets I use. Butfor that matter I agree to keep thepilot at 45

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