BKmod w/ Exhaust

15 replies to this topic
  • Zique

Posted April 19, 2006 - 07:57 AM


I was curious, I just put an exhaust on my 426. I am also planning on doing the bkmod tonight. Is this going to make my jetting way to lean that I can't just adjust it w/ the fuel screw?

  • Zique

Posted April 20, 2006 - 03:17 PM


anyone? will my fuel screw adjustment fix this?

  • jamieyz426f01

Posted April 20, 2006 - 03:20 PM


depends on what your current jetting is.

  • Fastest1

Posted April 20, 2006 - 06:12 PM


The BK/GB Mod only affects the accelerator pumps duration of spray.The theory is that the long spray was flooding the bikes and either flaming out or if not yet started, making sure it wont start by injecting too much fuel and wetting the plug. It shouldnt effect your jetting at all. It worked great on mine and many others bikes. Havent had any starting issues in years.

  • viking_in_wa

Posted April 20, 2006 - 07:18 PM


when i did my bk mod i also re jetted at the same time and was in my case a mistake. just do the mod and make an adjustable fuel screw and go from there. that may be all you need to do.

  • Zique

Posted April 21, 2006 - 06:29 AM


Are the adjustments w/ the fuel screw going to be enough to compensate for the new exhaust as well?

  • Fastest1

Posted April 21, 2006 - 06:40 AM


Dr.D pipes dont always require rejetting. I would put it on and run it to see. What year bike do you have? The BK Mod is thought to help the 00-01 models the most, others might benefit but I think Yamaha changed the accelerator pump diaphragm by 02 to lessen the shot. The fuel screw (if not adjustable to spot on) will at least compensate enough to be very rideable, it may not be optimum but it will run fine without causing any damage to the motor. Same with the main jet, if it runs now it should run fine with the Dr.D. You probably can go larger on the main but probably only one size, so it wont be detrimental. Enjoy!

  • Zique

Posted April 21, 2006 - 07:03 AM


I have the pipe on now and it is running very hot now. It is not Dr.D...it is a WB E-series. Jetting was perfect before I put it on, but now it is definitely running off. It is popping really bad on decel. Should I adjust the Fuel Screw in or out? Oh...the bike is a 2000.

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  • Fastest1

Posted April 21, 2006 - 07:18 AM


If it is popping on decel it usually means it is lean in the pilot circuit. Turn the fuel screw out in 1/8th-1/4 increments. If you pass 2 1/2 turns got to the next size up on the pilot jet. Why do you say it is hot?

  • Zique

Posted April 21, 2006 - 07:26 AM


I just mean it is boiling over...My bike does that when it runs lean. Sorry for my termonology.

  • Fastest1

Posted April 21, 2006 - 07:36 AM


All engines are hotter lean. I was really just curious if your response was to the header glowing red. That comes up alot here. Changing a pipe will allow some people to see their bikes running at night for the first time. Of course these bikes overheat quickly if not moving. If I were you I would buy the next main jet up in size and try it also. It might run stronger and if it doesnt, go back to one you have in now. You should be able to turn the carb sideways in the clamps enough to change the main.

  • Zique

Posted April 21, 2006 - 07:46 AM


Yeah, I can change the main w/o removing the carb. I know about the header thing as well. It seems like someone mentions it every 3-4 posts...lol. You really think I need to change the main instead of turning the screw? I want to do what is best, but I'll be honest, I hate dealing w/ jetting.

  • Zique

Posted April 21, 2006 - 07:48 AM


BTW, it will obviously be getting about 15 degrees warmer w/in the next two weeks. I guess I'll need to change just for that.

  • Fastest1

Posted April 21, 2006 - 10:31 AM


They affect 2 different areas entirely. The pipe is already requiring more fuel than it was as evidenced by the popping. The fuel screw will help that symptom. The main will give you more pull at WFO possibly. I am not saying it will, I am saying if you havent tried to next size up, how do you know if you have found the full potential? Jetting can be done pretty painlessly, it just takes patience. You are on the right track. Adjust the fuel screw to eliminate the popping. If you are happy with the performance at that point, dont do anything else. Being off 1 jet size will not hurt the bike at all but it could possibly run better. Dont know until you try.

  • Zique

Posted April 21, 2006 - 11:43 AM


Thanks fastest1 I really do appreciate the help. I think I will eliminate the pop and then wait the two weeks to rejet it for the temp change.

  • Fastest1

Posted April 21, 2006 - 02:30 PM



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