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the426master

jetting blurp

11 posts in this topic

my 426 is weard when you crack the throttle when the motor idleingit will always die even when I am going down hil and my motor is brakeing it will die if I crack the throttle whats up :)

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Master,

Yes a JD kit would help, but not with this issue. I suspect you are rich on the pilot circuit. If you turn the fuel screw in 1/2 turn this should fix the stalling.

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Master of the 426 I would suggest you look into the Power Now deal. I will say that having the right jetting will make your bike run better but will not always fix that bog. In my experience I don't think that you will ever get rid of that bog entirely. For instance if my bike is just idling on the stand and I wack it as fast as I can it will always bog even with the right jetting and the power now. However I have never had my bike bog on the trails while I was riding with the power now deal. We are talking like in the last 1000 miles if riding. As a matter of fact this bike is so fun to ride now because I can just give the throttle a little twist and the front end will get over anything. So the bottom line is in my experience the Power now really helped the first 1/4 of the throttle then the jetting will really help from there on out. But I don't want you to think that you are going to get rid of that bog from an idle to as fast as you can wack the throttle, that will most likely never go away. But I think that you will not notice it at all when you are riding. Let me know if there is anything else I am leaving out.

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Have you done any of the following

1: GBmod

2: Jetting

3: Clean the Carb

It appears something is amiss for sure. Issues could range widely but I would first look at the accelerator pump and make sure that is not damaged or is functioning properly.

If the pump is working, then I would consider the GBmod for you. This cleans up the accelerator pumps duration of spray and will stop the bog. But you stat it dies??

Are you mistaking Dies for a Bog

When you say it dies does the Motor just

1: Shut off

2: Stalls

3: Hesitates

If it is 3 then the GBmod will help

Or the Carb could simply be dirty and in need of a very good cleaning. One last item How clean is the Air filter?

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I will say that having the right jetting will make your bike run better but will not always fix that bog. In my experience I don't think that you will ever get rid of that bog entirely. For instance if my bike is just idling on the stand and I wack it as fast as I can it will always bog even with the right jetting and the power now.

I'm going to have to sort of disagree with you there.

I am continually confused as to why anybody cares what their bike runs like on the stand. For those who don't you should expect good, crisp throttle response in any riding situation, if you are not getting that your jetting isn't what it could be.

Unfortunately it isn't always easy to determine the problem based on short descriptions. Master, you need to verify that your accelerator pump is working properly, see if your jetting on the clip is maybe off, and set your idle mix properly.

Hope this helps.

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I am continually confused as to why anybody cares what their bike runs like on the stand. For those who don't you should expect good, crisp throttle response in any riding situation, if you are not getting that your jetting isn't what it could be.

i agree!when people complain about the bog i most always find they are talking about when it on the stand. :)

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You guys are right! When I first got the Bike the bog happened on the trails just as much as it would happen on the stand. Since then I have learned that you will never get it fixed on the stand but you can get it fixed on the trails. It just took me some time to figure that out. I mean lets face it you put your bike on the stand to work on it and do all of these trick mods that every tells you about and you go and start it (on the stand) and it is like you did all that work for nothing. But go ride it and it is a diffrent story. The point I was trying to get accross was that don't expect that you will get rid of the bod from a dead idle in neutral, shall we say. Sorry Hick.

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You mean we are supposed to ride these things, not just sit them on the stand and rev 'em :)

Just kidding :D If it is dieing on the trails still after the re-jet and all, try upping the idle just a hair. :D

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I have a power now ,it is rejetted, I did the bk mod well just look and my profile

Did not see GB/BKmod in sig that is why I asked.

Now for another round of questions

You have not defined dies as you put it

Does "the bike dies" equal to:

1: Stalls (aka Engine Stops)

2: Hesitates (aka engine blubbers)

3: ??? (aka Define Dies)

Next question:

Have you Removed the carb, cleaned very well including air filter?

Next Question:

Have you tried to adjust or fine tune the GB/BKmod ?

You can learn a little more finer points of the GB/BKmod here

GB/BKmod Explained

Or read it here

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

First I wish to say that this mod is entirely due to Brian Kinney, Garrett Berg is the first to have detailed and posted the mod to the Thumpertalk forum.

I am merely trying to explain the details on proper setup after the mod. Thanks Brian Kinney and Thanks Garrett Motoman393 Berg. Also note, the pics are from Garrett's site as well. I enhanced them for the settings detail.

**************************************************

Taken from Garrett's Web Site

http://motoman393.thumpertalk.com

**************************************************

Info:

This accel pump mod is ONLY for the 00'-02' YZ426, 01'-02' YZ/WR250F and 00'-02' WR400/426) this WILL NOT work on 98-99 YZ400's and 99 WR400's. When this mod is done correctly is will make your bike run and start better. It also will give quicker throttle response and eliminate the bog off the bottom. Your jetting will most likely need to be richened up since this mod shortens the duration of gas sprayed (from 1.7 secs stock to .3 secs)

The Procedure that Brian Kinney gave me:

Brian Kinney is Tim Ferry's Factory mechanic (and the originator of the BK mod) and these were his instructions...To limit the accel pump spray length you must drill and tap the pump cam stop and install a 4mm screw/spring combo. That will contact the pump cam. A hex socket bolt works well approx. 25mm long. Remove the subframe so you can look down the throat of the carb and with a stopwatch time the length of the pump spray when you stab the throttle. I usually click the stopwatch at exactly the same time I turn the throttle and click it again when I see it stop. It may seem weird but it works! Also you need to adjust the pump timing screw so that it does not hit the slide when it is raising. The timing is close when the spray just misses the slide. Then set the duration of the spray to .3 seconds with the adjustment screw you just installed. This may sound complicated but is the only way to get rid of the pesky bog off the bottom.

Helpful Tips from me:

You don't have to use a 4mm bolt I used a 6-32 1" long flat head screwdriver bolt. I also used a spring out of a pen that you write with. My stock pump timing was around 4.5 secs and now it is around .35 secs (maybe that was why is flooded easy and was sometimes hard to start when hot?) Also when drilling put a piece of metal (like a hacksaw blade) in-between where the drill bit will poke through and the black pump thingamajig LOL. The squirt of the gas was also off on my bike...it should spray gas so that it just clears the slide...but mine sprayed when the slide was about halfway up the stroke!

Just by starting up the bike I could literally "feel" the difference, it felt like the snap of a 250 2 stroke and didn't have any bog whatsoever! You will really be amazed by what $4 does to the performance of this bike! The jetting I ended up with: 168 main, 42 pilot (1 3/4 turns out), needle in middle position.

**************************************************

The below image shows the Mods main component. This is the duration screw added to lesson the duration of the fuel Squirt

Carb1.jpg

The Second image Describes the GB/BKmod in conjunction with the Accelerator timing screw. More of both these will be explained below.

Carb2.jpg

The 3rd Image is the side view of the complete mod and how it will work.

Carb3.jpg

The last 4th Image is a side shot looking somewhat down the back side of the carb. I will now explain the setup.

Carb4.jpg

**************************************************

So to begin, if you have not done the mod yet follow the mod completely as Motoman's instructions specify in the first part of this post above.

One side Note Very important. When drilling the 4mm hole into the Carb, place a thin piece of metal (Hack Saw blade) between the exit and the plastic cam.

**************************************************

In pic 1 I used a 4mm hex bolt, much easier to adjust.

Just set the bolt into place at first at the edge of the hole or just leave it out until the timing is adjusted.

Now for the timing

In pic 2 it shows the pump screw, it is important only to adjust this clock or counter clock wise in 1/8 turn increments. It is very sensitive and if you pump is working correctly you will see the spray change effectively.

Note Make sure the float bowl has Gas in it for this part, and don't do this near a flame

Take a look at pic 4, but you should be looking down the back side of the carb, keeping the carb as level as possible.

Turn the cam on the carb, you will notice a little brass nipple in the right corner just in front of the slide. This is the squirt nozzle.

If you twist the cam you will see a stream of fuel hit the slide as it opens.

THE OBJECT IS TO HAVE THE SQUIRT JUST START AS THE SLIDE LEAVES ITS BASE

so with that in mind if you turn the Cam and you see the squirt immediately hit the slide and the slide is not moving, you need to turn counter clock wise the Pump Time Screw 1/8th turn.

You should see an immediate effect on when the squirt starts.

Remember the squirt must start just as the Slide begins to open

Once you have the time done, it may take a few sets to get it correct. You can now work on duration. As you noticed the duration is long and the squirt has plenty of fuel.

So now comes the duration

I don't understand how the .3 or .5 duration stated, I am not that fast to hold a stop watch in one hand eyeball the spray and turn the cam at the same time. I am sorry but logic tells me unless you are a Cyborg, its impossible.

Anyway the way I did this is to visually adjust the duration by sight and feel. The 426 only needs enough gas to get rid of the bog, on the other hand not enough and you still have the bog (Fuel Starvation).

The Distance between in Pic 2 on my sled is about 1/8 of an inch. I set this by watching the squirt as I opened the cam up. I tried a couple of diff settings but found that all you need is a split second of fuel to get the beast to breath fire at bottom.

So that is it except that you may have to adjust it for you area of ride, altitude, humidity, and weather will effect the GB/BKmod. It does take some time but to adjust and get correct is a big payoff on the 426.

I used the Hex Bolt because once I was able to get the Mod complete and the bike back together a simple quick adjust to fine tune in the woods was perfect.

Again, it is a great mod, it can have dramatic effect on your ride if done correctly.

Hope it helps

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