Two more BK mods completed!!

Myself and Pat(KC Husky)completed the BK mods on our 01'426's Saturday night. Both of the bikes responded well. They both revved quicker and felt better in response. Our jetting is different between the bikes..wanted to poll some of the jetting guru's here.

Mine 45pilot/165main/1 richer on the clip/1-3/4 fuel screw

Pat's stock pilot/168main/1 richer on the clip/same fuel screw.

Both bikes set at around the .3 mark, neither bikes pump stroke hitting the slide.

Pat's bike started 1st kick, mine took about 5-6, mine has been sitting for 6weeks due to broken toes/drained the tank though. We both suffered a cough if the throttle was whacked wfo. If given moderate it wouldn't, just wondering if this condition would be felt while riding?

Also, I tried to give mine 4 half/hearted kicks last night and it wouldn't light, the last kick resulting in a loud back fire. Could the carb/cylinder junction be off?I know if may need a new plug. Mine also has a years worth of riding on it, but Pat's just sounded better/smoother? Just wondering, we will both tinker and adjust to fine tune throttle response, any tips appreciated. The temps we have had are in the 60-mid 70's range and damp. Thanks, Jason

I did the BK (BurgerKing) mod too this weekend. After the bike was warmed up, If rolled on the throttle to quick (snap it),I would either die out or back fire. I turned up the idea screw and this helped a lot. As long as I give it a little gas beofre I open the throttle all the way its fine.


01 WR426 Uncorked.

Jason: Why are you guys one clip richer on your needle? Did this help whatever carb glitch you experienced at the time? My initial feeling is that your cough/hesitation might be due to this. But before you make and clip changes, try a few smaller adjustments first and only move the clip if everything else fails. Try making very small leaner adjustments on your pilot fuel screw. (On your particular bike, you might want to take the time now to check your valve lash. You might have a valve or two that are a wee bit tight). It's possible to get the hesitation eliminated but it takes patience along with trial and error.

Jason in KC where in kansas city are you located? and where do you ride at have you ever been to the St Joseph Track(knobbyhill) or kingsville?

Wow! Kansas boy's

I'm in Pittsburg to your south. You know the buttcrack of Kansas. It's hard to find places down here to ride without trespassing. Got any good places up there to ride? Let me know!

Thanks, Scoredaddy

I overjumped a tabletop and buckled my ankle on landing last friday. First time I have ever hurt myself and not crashed. So I had time to do the BK mod too this weekend. I have not ridden it yet, but I was also disappointed to see that my bike will also die if the throttle is whacked open on the stand. No different than before. Hopefully an actual ride will show a difference.

I have a great way to set the timing. I videotaped the AP jet squirt, and played it back frame by frame. My videocam is 30 frames per second, so you want it to last 9 frames. Made it very easy to get it exact. BTW, mine was 2.7 seconds stock. I left the delay alone. It seemed pretty close stock, it seemed like it made a difference on how quick I whacked open the throttle, to "just missing the slide". Any tips on setting this?

"I turned up the idea screw"

Now that's something I've not been able to find on the WR :) Just kidding! I'm looking forward to other good stories of this mod so I can convince myself to take a drill to my carb!

I too did the carb mod this weekend but have yet to ride the bike (I was on the Mountain Bike all weekend). I did start it and is started fine. One thing to remember, especially as the weather gets colder, is the prime sequence Yamaha recomends. 1-3 twists of the throttle (depending on temp) will not produce nearly enough prime after making the Burger King (BK) mod. Logic would say that if you reduce the spray from 1.5 sec to .5 sec that you may need almost 3 times as many throttle twists as normal for cold starts. I think at least twice as many for sure.

Another KC Boy here. For riding areas we go Merwin/Drexel, MO to the MX/Harescramble track we have there. As for the KnobbyHill track keep meaning to get there as I hear it is a great new track. I think that Jason and some of the other guys have been there this summer.


You gonna have to let me ride your blue beast since the mod and the suspension mods.


Scott #410

Some Fear Racing "Cause if you don't have any you ain't going fast enough"

'99 YZ400F(Coming to a Theater near you soon)

'92 ZX-7R and '97 ZX-7RR

"Doesn't hurt till the bone is exposed"

"When cut do you bleed green? I do!"


wow you live in grandview? i live in smithville your like 15mins from me

Many individual persons' initial input pertaining to going to Burger King BK mod) were very, very positive. I was just about to make the punch mark on the boss of my carb when this post came up.

I have an '00 426 that has the P38 (crap) carb bottom. The part is not as "Factory" touted it. It did seem to help somewhat, but I still had to deal with the cough at T.W. (throttle whack). Through some jetting changes and accell rod adjusting, I can still make my bike hesitate/cough on the stand, but it rarely does on the track - and that is a track where there are a lot of jumps. On true outdoor type tracks I do not notice any coughing - only vary rarely.

One way to keep the cough away is to always keep the motor "perkelating" - in other words I never lay completely off the throttle - unless I'm using full engine breaking. When I enter a turn, I roll the throttle to make sure the engine knows I'm about to summon WOT - no problem. Interestingly enough, when I'm in the air - and about to land I start my throttle roll just before contacting the ground - this protects me from being thrown over the bars if I land in too high a gear (cough / engine complete shut down), plus it brings up the RPM to avoid the cough, and it puts the engine RPM in the range where I want it - just where full throttle (read: ROOST) is at my command.

The adjustments (from 2-smoke) I've made in the way I ride, along with inconsistent results from going to Burger King make me wonder if the mode is worth it.


I never lay completely off the throttle - Interestingly enough, when I'm in the air - and about to land I start my throttle roll just before contacting the ground - this protects me from being thrown over the bars if I land in too high a gear (cough / engine complete shut down), plus it brings up the RPM to avoid the cough"

Boomer, if you do the BK mod you will never havta do any of the above mentioned stuff again. I can't imagine having to worry about my bike coughing when I land. :)

Last night I raced and over-jumped a big stepdown triple and landed on flat. Major impact and the only thing that saved me was the great suspension and instant throttle. I had a perfectly running 01 that is now more responsive. You will not regret it, just do it!!! :D


Moto to Live

Live to Moto


Hey G-Man what jetting did you end up with? How did you like the 168 main? Later,



I get my kicks on a 426!

Motoman393's MX Site

Sorry for not getting back on here sooner, had to work from home and our remote server was hit by that virus..anyway, I have the cough still while on the stand. I went back to my previous settings,ie, 42pilot/165main, stock clip still has the cough..I never noticed that I had it before I did the mod cuz I never whacked the throttle while sitting still. I did take it up the street and didn't notice it..could it just need to be under a load keep from coughing. I adjusted the ac pump screw in and out w/no changes...could I need to be leaner on the clip?

I think the cough problem is the carb can not deal with the change from the idle circuit to the full open curcuit.

I did not get to ride this weekend to fine tune my setup. But, in my garage as I started riching the idle the cough got better.

With the BK mode, the delay in the accelerator pump as been increased, in most cases. This means it does not give you as much help as before to get you off idle.

Currently, I am running the stock jetting. I am going to play with the delay and the fuel screw to see if I can get the cough to go away



01 YZ426F #85 Vet C

Hey forloop, I saw on another post where they adjusted the delay/timing screw a 1/2 turn clockwise to get rid of the cough. That is the scew in the carb from the factory behind the black plastic above the ac pump screw we just installed. Maybe mine is off some and it's getting the squirt of fuel too late to handle a quick increase on throttle position. Easy adjustment and quick, will try it when I get home today. Now the fall temps are coming in and our highs are in the upper 60s and 70s, prime riding!!

"Why did you have to mess with? It's practically a new're always messing with it!" - Things our wives say.

Jason, I would dump that carb and go with a Dellorto! Much easier to work on and since you can't get parts or advice you won't want to mess with it at all.

See you tomorrow!

hi guys,

i'm pretty new to this sight so bare w/me. i have a '01 426 and would like to get this mod done, does anyone have pictues of each step?


tim in ca.



Tim in Ca. Just go to motoman393's web page. He's posted detailed instructions with pics. Very good info.


00 YZ426F

01 TT-R125L (my son's)

74 Hodaka Super Combat(gone but not forgotten!)

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