BK Mod queston for YZThump



31 replies to this topic
  • forloop

Posted August 28, 2001 - 03:10 AM

#1

Hi,

I just wanted to know if you had to change you jetting when doing this mod.

Thanks,

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Rick
01 YZ426F #85 Vet C

  • YZThump

Posted August 28, 2001 - 03:31 AM

#2

The first couple of straight line runs the bike seemed that it was starving for fuel up high,so I went up on the main to 165 and kept the fuel screw at 2-out with the stock pilot.It really pulls all the way thru now.And obviuosly if the motor was running that rich its only a matter of time before carbon becomes a problem.If you do the Mod and for some reason you don't like it,you pull out the screw and no-one ever knows that it was done(No way I'll take mine out)its just that much better!!When I put the new pipe on it was a jetting nightmare with DSP"s jetting specs,I finally ended up back at stock and it wasn't fouling any more plugs,now with the Mod I see a better improvement all the way across the power range!! Good Luck!

  • blaze

Posted August 28, 2001 - 03:27 PM

#3

i just finished the BK mod and noticed a big difference starting the bike and 1/4 throtttle all the way thru the top. my timing was way off also on the slide. shooting when the slide was in the middle. the duration of the squirt is betwenn.3-.5 sec. my problem is a falt spot off the start of the throttle, it almost cuts the bike out. also i was wandering if by leaning out the bike like this would cause any excess piston wear. my main jet is 152 1 clipp lean on the needle and 1 turn out on the pilot. 2001 yz 426. any info much appreciated. -thanks, alex

  • blaze

Posted August 28, 2001 - 03:29 PM

#4

and im at 8000 feet, 70 degrees. thanks

  • flyinguitars

Posted August 29, 2001 - 03:37 AM

#5

Does this mod help overall performance? I have an 01' that runs fine and starts good. I was wondering if I did this mod, would I see an increase in performance or is this just a throttle hiccup/sooty plug/hard starting fix?.
Mike

  • Scott_F

Posted August 29, 2001 - 03:47 AM

#6

Blaze, it sounds like your flat spot off the bottom may be caused by the delayed pump squirt. Have you tried adjusting the delay screw?

If the timing is good, like the squirt is just missing the slide as it opens, maybe a one size bigger pilot jet would help. Let us know how it tunes out.

[This message has been edited by Scott F (edited August 29, 2001).]

  • forloop

Posted August 29, 2001 - 03:53 AM

#7

blaze:

Your bog is one of teo things, a lean condition or rich condition. You most likely have done two things when doing the BK mod. First, you have changed the pump timing and second the pump duration. Pick on of these and change it and see if it helps. Then try the other. Dialing in a carb is a try and test sort of thing. Anyway, that is what I would do.

ScottF was typing the same time I was. I total agree with what he said.

flyingguitars:

I would not think it would help constant speed stuff. The pump only comes into play when you twist the throttle. It helps with acceleration. It will not give you more HP. It could help a lot with all the problems you mentioned. It is similiar to having a rich needle setting. OK on top and bottom, but the middle is messed up. Well the middle when turning the throttle is messed up.


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Rick
01 YZ426F #85 Vet C

[This message has been edited by forloop (edited August 29, 2001).]

  • YZThump

Posted August 29, 2001 - 04:14 AM

#8

hey Blaze,
What pilot jet are you running??? I'm thinking out loud ,if your that lean on the Main and running the Stock Pilot its too rich down low,thats when I had most of my "new pipe problems" when I was too rich down low fouled plugs or just real sluggish with the "bog". I'm at Sea Level so 165 MJ and a 42 PJ with 2-turns out works for me
The Pilot and Adjustment Screw can change things quite a bit! Where as the MJ changes don't seem so drastic.

[This message has been edited by YZThump (edited August 29, 2001).]

  • Jason_Williams

Posted August 29, 2001 - 10:57 AM

#9

just left a detailed account of my testing on the WR 426 side. check it out and let me know what you guys think?
Jason

  • blaze

Posted August 29, 2001 - 03:15 PM

#10

hey guys, i just went for a ride and i am amazed at the difference! i dialed in my pilot screw to 1 and half turns out, which helped alot, but still a slight flat spot right on the start. i may check the timing of the squirt and just make sure its missing the slide. besides that my plug looks good and she feels beastly. next i may try one of those fmf Q's just to quiet her down a little. thanks everyone-blae

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  • Scooter426

Posted August 30, 2001 - 02:34 AM

#11

Just did the BK mod to my '00. It was way off in duration, but the squirt just missed the slide when I whacked open the throttle. A note to the others wondering if they should do this, this mod will dial in your accel pump which operates whenever you roll on the throttle , whether revs are high or low. It will help any time you want to accelerate. My duration was 3-4 seconds before the mod (.3sec is optimum). I am waiting on jets from Lockhart to test the mod in action on the MX track. I will keep all y'all updated. I have an FMF Silencer/Stock header, 165 main, 42 pilot, 1 3/4 turns out on air screw, at sea level, air box lid removed.

-Scooter
'00 426/'01 Susp front and rear

  • ricky1

Posted August 30, 2001 - 05:01 PM

#12

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Has anyone read my recent post's, both here and on the WR side? I know nothing compared to James Dean, but I spent many,many,many hours on this. (With J.D.'s help)
posted August 27, 2001 06:15 PM by John in Granite Bay WR Side; "Monty and Friends"

--------------------------------------------------------------------------------
"Rick,
It was great meeting you. Thanks for the offer to ride your 426. It was the first time I've ridden one. Within 20 feet it felt sooo comfy as the front end eased up ever so gently. Sorry about the 4 gear wheely! Your jetting is spot on. Look forward to riding with you again. Maybe up in Tahoe sometime???"

I live at 6300ft,at Lake Tahoe. If I ride downhill, I drown. (Average depth of Tahoe is 1645 FEET!) My 3-4 time weekly ride is from 6300-9000ft, and this is what I jetted my bike for. However, John's post refers to a ride from 2500-4000ft.
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Rick Fuller
'01 yz426
'00 yz426 destroyed by fire in desert race 4/22/01
'81 490 Maico

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Rick Fuller
'01 yz426
'00 yz426 destroyed by fire in desert race 4/22/01
'81 490 Maico

  • forloop

Posted September 01, 2001 - 10:38 AM

#13

I just finished up doing the BK Mod. My stock settings were 2.2 second duration and the delay was zero, stream hitting slide.

I adjusted the duration to .5 seconds and changed the delay so the stream missed the slide.

First test ride on the street, wow, noticeable difference. The front end likes to come up now.

I did notice that right off idle, less than 1/8 throttle, the bike had a hesitation in it. I started opening up the fuel scew and that seemed to cure it. My staring position on the fuel scew was 1.5 turns out. It might by two turns now. I have not checked were I ended up.

I am still playing with it to get the fine tuning in, but two thumbs up for this mod. Can't wait to get to the track. If I only knew a good anti-rain dance,

Later,


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Rick
01 YZ426F #85 Vet C

  • YZThump

Posted September 01, 2001 - 03:06 PM

#14

hey Rick,Wheelie's are a definite!!!! I have a little bog going on too,when you try ,.it will happen.I've practiced Hare Scramble starts and when the motor is warm it doesn't seem to be a problem,but its always in the back of my mind when I start and go in a hurry!! I wish I had a track out the back door to test and tune,I know I could fix it! Let me know what your jetting is,I haven't richened the needle yet and might go back on the fuel screw about a 1/4 from 2 and see what thats like.Ya gotta love the way it pulls just from the mod.!!!!!Talk about a BARK!!!

  • forloop

Posted September 02, 2001 - 10:52 AM

#15

I got ride of the 1/8 throttle hesitation by turning the delay screw 1/2 turn clock wise. I need to pull the subframe and see were the stream starts now. I am about 1.75 on the fuel screw now. Very crisp throttle response good off idle response.

Yzthump, here are my current settings.
I have 158 main, third clip, stock pilot, 1.75 fuel screw, and .5 second duration. Houton, Texas.



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Rick
01 YZ426F #85 Vet C

  • G-Man

Posted September 02, 2001 - 12:03 PM

#16

Originally posted by flyinguitars:
Does this mod help overall performance? I have an 01' that runs fine and starts good. I was wondering if I did this mod, would I see an increase in performance or is this just a throttle hiccup/sooty plug/hard starting fix?.
Mike


You too huh Mike, I am so CONFUSED NOW on the BK Mod. On one hand, everyone raves about better throttle response, but there seems to be a lot of different opinions on jetting, hesitation etc.

Questions for a 01 426 at approx 1500 ft (AZ)

1) Is this mod worth doing or will I be opening up a can of worms, with jetting woes. My motor and jetting, pipe are bone stock and runs great!!! Hesitant to mess with a good running m/c ya know?

2) I have never jetted this bike, which jets would I need if I did this mod?

3) Will I get a never before "Hesitation"?

4) I would like my bike to bark more outa corners, is this where it really helps?

5) Do I need to take the carb out/is it a hassle to do?

thx for your help,




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Moto to Live
Live to Moto

http://www.geocities.com/gmann_3000/

G-Man

  • YZThump

Posted September 02, 2001 - 12:17 PM

#17

G-Man
If you are skeptical at all,at least take off the subframe and stab the throttle while looking down the throat of the carb,You won't believe the amount of fuel being unused take off your pipe and see how much carbon is in it.Mine ran great until I put a new pipe on it and then tried to jet as per the Pipes manufacturer and it was way to rich,after struggling with jetting I was gonna return to Stock Pipe which basically had the same bog area as I have now.I figured what the hell I'll do the BK mod and if I don't like it I'll take the screw out and put the stock pipe back on.After doing the mod ,I'm really happy with it,Just Do IT!!! Its really easy--at least look at the fuel squirting down into the cylinder,I'm amazed it ran at all like that!!!! Look at the WR when they cut the grey wire how it improves the way it runs!!!

  • motoman393

Posted September 02, 2001 - 02:04 PM

#18

G-Man,

First off let me say...I was in your same position whenever I was trying to decide to do the mod! My bike already ran awesome (no hiccups, fouled plugs or anything, it ran GREAT!!) But we are all "crazed MX freaks" and we want the most out of our bikes. Right? (at least I do)! After doing this mod it is Unbelievable how much faster my bike is than before. I have a few riding buddies that have 426's... and before the BK mod my bike was about the same speed as theirs (in a drag race) but after the BK mod I immediately pull 3-5 bikes lengths on them and keep pulling until I'm pinned out in 5th (and by then it like 25 bike lengths)! At the track it is Great I just keep it in 3rd and BRRAAAP my way around the track, because Bottom end is what the BK mod gives you! Now let me answer your questions:

1) Is this mod worth doing or will I be opening up a can of worms, with jetting woes. My motor and jetting, pipe are bone stock and runs great!!! Hesitant to mess with a good running m/c ya know?

It is the best $5 I have spent on my bike! If you dont like the BK mod simply take the screw out and it will be back to stock!

2) I have never jetted this bike, which jets would I need if I did this mod?

Im still at stock jetting the only thing I did was richen the fuel screw up a 1/4 turn (now it is at 1 3/4 turns out)

3) Will I get a never before "Hesitation"?
I doubt it...if you do it can be eliminated by fine tuning the jetting!

4) I would like my bike to bark more outa corners, is this where it really helps?

OH YEAH...bottom end is what this mod is all about!

5) Do I need to take the carb out/is it a hassle to do?

It sounds like a hassle...but it is real easy (takes 15 mins)! I have found that it is quicker to take the carb off the intake manifold and intake boot and have the carb hanging by the throttle cables off the bike! You have to run a longer fuel line to the carb if you are doing it by yourself (or use the stock line and have someone help you) By taking the carb off this way you dont have to remove the subframe, and you get a more accurate reading IMO (it also doesnt fill your cylinder full of gas like the other method does)! Hope this helps answer your questions. If you have any more questions just post them! Later,

Garrett
BK Carb Mod Pics and Info


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

  • forloop

Posted September 02, 2001 - 02:55 PM

#19

There is no queston that the acc. pump is using too much fuel. This mod allows you to tune the accelerator pump duration. With the mod you can go from stock to zero duration.

You can already adjust the delay. So, do the mod and adjust it to get the best throttle response. If all you do is tune the duration some that would be a positive thing.

In fact, I am not going to change my jetting, I am just tunning the delay and duration for optimum performace.

Good Luck,


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Rick
01 YZ426F #85 Vet C

  • G-Man

Posted September 02, 2001 - 07:01 PM

#20

Thanks guys, looks like it's on the "must do" list.

Garrett, those are some great pics! On the pen spring: Are those two springs separated by a washer?

What size tap and thread did you use?

G





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