Jetting...Where do I go from here?

Here are the details, where I started and where I am at. Hopefully, the experts here can point me to where I should go next.

A couple weeks back I purchased a 99 WR400. It came with both the stock & a Big Gun (SA) exhaust, the BG was installed. It was all stock except for the throttle stop mod and it had been jetted by one of the local tuners.

I am in Colorado Springs, altitude ~6000ft and will be riding mostly here and around Woodland Park ~9000ft once they put the fires out. Temps lately have been in the high 80s and not much humidity.


PJ = 45

PAJ = 75

SJ = 60

MJ = 158

MAJ = 200

FS 2 turns out

Needle = DVR clip 3rd position from the top

Bike starts one kick when cold. Not much experiance starting it hot since most of my riding has been on the street trying to sort the jetting out. Hence I work on it, ride it around the block, let it cool off to work on it some more... With the bike basically stock, this jetting seemed lean. The engine gave off a lot of heat (not very scientific I know) and it popped a lot if the throttle was closed. It needed the choke to start first thing and would not idle without it. It would not idle well once warm.

I then jumped in last weekend and performed the remainder of the mods in my sig.


PJ = 45

PAJ = 75

SJ = 65

MJ = 158

MAJ = 200

FS 2.25 turns out

Needle = DVR clip 3rd position from the top

Bike still starts on the first kick when cold (with the choke). I can take the chock off much sooner now and the bike will idle both hot or cold. There is less popping when the throttle is shut. However, when I whack the throttle open from closed or from anything less than half open, falls on it's face, no wheelies here. My first instinct is to lower the needle one notch (rsie the clip to position #2), but I though I would ask to see if the PJ/MAJ might also be a player here since I have not changed the pair to YZ specs.



Your main air jet, I believe, is waaayay to large, if indeed your mainjet is a 158.

Although I ride at 1000 feet, look in my signature for my jet specs.

Don't jump on my jetting.

Taffy or James Dean are THE experts on this. Taff is in England and he has his time differences. You may try to PM him. Just post a search for him under the WR400 forum. You can then find a posting from him and send him a PM.

Best of Luck. We will get you fixed here!!


The higher your elevation the leaner the fuel to air mixture should be. I’m at sea level and am dialed in good. In your case, Taffy or JD will recommend leaner jets than what you currently have. Work with either of them, they are the pros.

Also, a useful tool for getting your jetting dialed in:

[ June 29, 2002: Message edited by: tk421 ]

It looks like the previous owner or shop set it up with YZ400 jetting except leaner for altitude. This is where the DVR came from.

The stock YZ400 main was a #175 with a DVR needle while the WR was #168 using DTM.

Considering you have opened the bike up some and are still using the #200 main air jet, try a #162 or #165 main jet. The #158 seems excessively small with the Dxx needle. This is considering the DVR needle leans the full throttle jetting more than an Exx needle. Stay on the same clip position #3 until after the main jet change, then if you still have a lack of pull, try clip #4.

You might want to get a DVP needle to make the off idle response a little better. This is a small change that should still suit your high altitude riding.

I made the jump to the 165 MJ and it did improve things form 1/2 throttle on up. It is still weak in the 0 - 1/4 range. Since I have to order all of these parts, should I be ordering a PJ/PAJ at the same time I order the DVP needle?

And thanks for the replys/input.

That's your choice, things will start to get more complicated with the extra variables of PJ/PAJ/fuel screw. See how the DVP performs first, it is a '98/99 YZ400 optional needle.


Took the new "Buddy Bike" YZ400F out for it's maiden voyage...Man this thing hits hard now. As I thought The EKN Clip 3 resolved most of the off idle hesitation....I will clear the rest up with the P38 I ordered friday. Wheelies in 1.2.3. and 4th gears. I think that I'm going to drop to a 168 main to get a little more consistencey in the upper throttle range...It felt mabe just a tid bit fat up top.

Also got my buddies DRZ 400 carb completely dialed in now....He is finally happy with performance...I wish he had come to me with it earlier instead of listening at the wannabe's at the dealership....

Thanks as usual.

Bonzai :)

Thanks Taffy, you are going to force me to think and I suspect this is where I will become really confused!

Just for fun (based on an earlier suggestion) I raised the needle one more clip and took off around the block. I can now loft the front wheel if I hit it from about 3/8 throttle to WFO. There is still some confusion at the lower throttle positons. When crusing in the 1/8 to 1/4 there is a bit of a stumble or hesitation and it still does not like to be whacked open from fully closed (though this is much improved). Last, I have not gotten rid of the popping when decelerating.

I know I really need to get off road and ride this a bit to get a better feel for it in a setting other than terrorizing the neighborhood.

Current settings @ 6000' 92* and around 20% humidity:


PJ = 45

PAJ = 75

SJ = 65

MJ = 165

MAJ = 200

FS 2.25 turns out

Needle = DVR clip 4th position from the top

old novice

i agree with JD about the needle selection. DVP is a good one for your altitude and if you ever work lower the EKN (or any **N) yamakazi has would be ideal.

the BOOOAAARRR noise is rich. i would shorten your APJ and play with the fuel screw for best snap response.

the big difference between JD and i, is that i like much leaner (but not lean) PJ settings. so i would suggest that you try a 42PJ.

this is for your own brain; if you raise the needle lots it's the same as going up one PJ size and vice versa. so if you raise the needle one or two clips for MIDRANGE you can most definately go to 42PJ.

remember that each one kicks a chain reaction.

higher MJ?

lower needle position?

PJ WAS rich so will now be OK?

just a scenario.


[ June 30, 2002: Message edited by: Taffy ]


You and I both have the same issue with whacking the throttle from dead idle. The resolution is adjusting the Accelerator pump squirt length and duration. On my WR it's 4 seconds and almost hits the slider, On My YZ it's 5 Seconds and blasts all over the slider. The fix as Taffy has aluded is to adjust the rod and the diaphram movement. You can do it the manual way (Drilling, inserting a bolt and collaring the rod) or by installing a P38 (which is the route I'm going)and trimming the rod.

Glad to hear your jetting is coming along.

Bonzai :)

YAMAKAZE, if you collar the rod you don't need to drill anything. the result will be the same as a p38, only adjustable.

The problem with the YZ is both duration and distance of the squirt. puting a colar on the rod will solve the duration issue but not the distance issue. The squirt is splshing all over the slide at the moment.

Bonzai :)

Ah yes, yet another variable to play with. This is much more entertaining than jetting 2-strokes. Actually, I have already added the collar, but have not yet tuned it. Based on archive research I set it at 2mm of stroke (down from 3mm) and have not taken it to the stopwatch level of tuning...yet. I suspect I am going to have to go there soon.

YAMAKAZE, I understand how to tune the duration, but how are you adjusting the squirt distance/direction?

The BK mod requires that a hole be drilled and tapped in the bottom of the Accelerator pump housing. a screw is then inserted and adjusted inward at one MM increments which limit the compression on the pump diaphram , limiting the diaphram stroke thus shortning the length of the spray without affecting the duration which is adjusted on the rod.

The P38 does the same thing without the drilling , tapping and screwing......It make's it easier at a cost of $65.00 .

I ALMOST FORGOT: There used to be a practice track setup just outside the Back gate (Widefield) entrance of FT Carson, that a bunch of us used to practice at...It was right next to the interstate... Is It still there?

Bonzai :)

[ July 01, 2002: Message edited by: YAMAKAZE ]

The BK Mod does not drill the accelerator pump housing cover.

The BK Mod drills and taps a tab on the outside of the carb body near the pump linkage on 2000 and newer Yamaha FCR's. Then a screw and retaining spring are used to set the linkage stop point for the pump stroke. The P-38 cover also limits pump stroke by replacing the cover with one that reduces the diaphram movement within the P-38 cover.

The '98/'99 FCR carbs can use a locking collar on the rod within the rubber boot to limit the stroke (Taffy Mod) with the same results. The collars are the same as some Remote Control (RC) airplanes use on their axles.

Bending the forked linkage on the '98/'99 FCR will set the point at which the pump starts to squirt. This can be adjusted to have the fuel miss the slide if you want by adding about .5mm freeplay. Most riders want the pump immediately from idle for a more instant response.

The 2000 and newer FCR carbs come with a screw on the linkage to set the pump starting point (also called "touch point" by BK).


Yes, I'm with you now, that's what it looked like you were talking about. We have no shortage of options.

'00 and newer- BK Mod, P-38, KL Mod, Leak jets on the 250's

'98/'99- KL Mod, Taffy Mod, P-38, Pinching the linkage


What did the DRZ jetting end up at??


it sounds a bit excessive to do the P38 or KL mod. both require surgery.

how hard it squirts and where it squirts aren't really an issue. i'd be delighted if the APJ hit the slide-yipee! it breaks up the fuel.

Taff mod and nothing else, that's all you need.

sometimes things can appear too cheap and too simple.



The final jetting on the DRZ wound up:

SJ 60/PJ 45/PAJ 75/MJ 168/ MAJ 200/OBEKN #3/and 3/4 turn on the FS

Additionally I deoctopused the carb as well.

The bike also has an aftermarket Yoshi Pipe as well.

The bike now hits hard all the way through the power band. and 4th gear Wheelies.

The owner has called me atleast 6 times to tell me how happy he is with the performance of his DRZ now.

Again thanks for the jetting training during this past year....I think I'm getting the hang of it now.

Bonzai :)

YAMAKAZE, this may seem like a silly question, but as I am after the same "lessons in jetting" from all of you here I am going to ask it anyway. Does the DRZ run the same carb we are talking about here on the WR/YZs ? I understand the updates with the Y2K Yamahas and why I can't do the BK, but is sounds like you are doing the same tuning exercise on the DRZ.

Also, it looks like any further tuning on the WR will have to wait until parts arrive. It's a shame no one bothers to stock more than just main jets (and I already have a colleciton of those thankfully).

Still trying to learn and understand...

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