BK's Carb mod jetting question

6 replies to this topic
  • MrMXer

Posted May 24, 2001 - 03:06 AM


I made the carb mod as described by BK last night to my scoot. Ran out of daylight to finish tweaking the jetting, but the bike seemed much more responsive. Where I am at is a 168 main, 48 pilot, needle is 2nd groove from bottom. Fuel is squirting for about .3 - .5 seconds. Real hard for me to get a better measurement than this. I also adjusted the timing of the squirt so that the slide appears to be aprox. 3 - 4mm above the nozzle when the squirt takes place. Still need to tweak the mixture screw on the bottom of the carb. Is this the ballpark area of where you guys are that have done this mod? I did notice a problem where the bike would seem to be idling just fine and then just shut off. Thought this might be caused by it being a bit rich at idle, but ran out of time to tweak more. I'd like to hear from some others who have done this and see what they have found with jetting. (One note: the only other mod to this bike is a WB ti header pipe and CF silencer)

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  • SUnruh

Posted May 24, 2001 - 05:29 AM


how about some pics of your fine work?

  • vznx1w

Posted May 24, 2001 - 06:44 AM


Your idle and mid jetting is richer than what I'm running with a WB E-series SS pipe. I've got a 168 main (like you)but, my pilot is a 45, fuel screw is 1 1/2 turns and the needle is on 3rd from bottom. Also, your stalling may be a combination of overly rich idle and idle speed being too low. The 426 has a tendancy to take a while to stabilize at its idle. In other words, it will idle fast for a several seconds before gradually reducing down to idle. If your idle is too low you might stall after a few seconds.

I'd recommend tweaking the fuel screw to get the best idle and making sure your idle speed is at least 2000rpm. Then start testing your new accel pump limit screw setting by whacking the throttle and noting response. Change the screw setting 1/8 turn at a time until you get the best response. 1/4 makes a huge difference so make sure that you don't over do and get lost--otherwise you'll have to remove the subframe and start over with the stopwatch method. You probably won't totally eliminate the hesitation during a sudden whack while idling in neutral. But, on my bike, I've never felt a hesitation while exiting slow turns since making this mod. Good luck.

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  • flyinguitars

Posted May 24, 2001 - 06:57 AM


Is this mod recomended for the '01 426?

  • MrMXer

Posted May 24, 2001 - 07:46 AM


Thanks for the Insight VZNX1, You have confirmed my suspicions on being rich. I thought it best to start rich and then work my way lean though. I'll have to pick up a 45 pilot and see how that goes.

I will take some photo's and post them at some point. The mod is pretty easy to do, but the tweaking takes some patience. And Yes, this mod is for an 01 426.

  • James_Dean

Posted May 24, 2001 - 02:15 PM


I also did the modification and use the #48 pilot but at 1 turn out, and prefer it over the #45. The needle clip is at #5 also (3rd from bottom). The clip position you are using is probably too rich.

  • MrMXer

Posted May 25, 2001 - 05:13 AM


Ok, Here is the skinny... As I said, it was getting dark and had to stop my progress on jetting. Turns out that my fuel line was pinched and the bike would actually start to go lean and then shut off after a minute or two. The swivel at the carb was pointed down which made the fuel line do a 130 degree bend. (Ok, I'm red faced) After fixing that, everything went fine. I did a few laps as I made the following adjustments; Installed a 45 pilot, adjusted the mix screw to about 1 1/2 out, decreased pump squirt by about 20 degree's of rotation on at 4-40 screw (4-40 stainless screw is what I used for the stop), and that seemed to be a touch better. I am still richer on the needle by one clip than you two. I plan to raise the clip back to the center position, test that and then drop in the 48 pilot like James and see how that goes. I still have a very slight bog when the throttle is wicked open fast, but the engine does not die. The bike is much more responsive at low throttle positions. This is a very good mod.. Thanks for the input all !

[This message has been edited by MrMXer (edited 05-25-2001).]

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