Wr/YZ jetting nightmares

Some other folks have said this before and I would like to reiterate this fact: It is very easy to jet too rich. Both my buddy on a YZ426 and my WR felt jetted correctly, and we both couldn't start the bikes due to plug fouling after about 60 mile over on several rides. We both made changes, not too radical, and ended up rich with the fouled plug as the witness.

I think the 50 pilot jet idea on the '00 is terrible advice, even the 48 ran very rich over time. I even fouled it with a 45/172/4th clip sotck needle and the pilot screw way out 2 3/4 (Wr time, airbox lid off, exh. baffle removed;600 feet 70 dgrees, low humid). Guys if you are running a 50 check your plug!

Someone mentioned recently that the bike should start on choke, rev up a bite and run crappy for the first few miles then run better as the engine fully heats up. I definately agree with this, my overall jetting seems better when this happens, and all my other bikes behave the same way. I think I am going to start draining my carb after riding-less chance of having fuel slosh while trailering.

Just to note: my jetting specs are now: 45PJ, 170MJ, 1 7/8 Pilot screw, 4th clip stock '00 needle. It runs good, will do a plug check before I have to this at the track again! ('oo wr timed, restictions removed, 600feet, 70 degreees, low humid), but I think this is close.

I always turn off my gas about 1-2 minutes from finishing my ride and burn most of the stuff in the carb and don't have a problem.

Here in Phoenix we have no jetting woes. The altitude changes are minimal and the humidity consistent. I suppose when its hot and we ride up on the rim at 7-9000 feet I will make some adjustments. BTW I can't tell a difference with my airbox lid on or off aside from the noise.

I have more 'fouling plug nightmare' stories than I can possibly tell you in a few minutes. In fact, from last March when I got my WR to about mid to late summer, I replaced plugs about every ride. Sometimes two plugs per ride!

Note though that I run at a much higher altitude than most of you (4000 to 13000 feet).

My 'non expert but experienced in jetting woes' advice would be this: Get your bike running good first. You can probably do this with the stock settings or only minor changes from the stock settings.

Then start experimenting with bigger mains or needles or pilots etc etc etc if you feel like you want to do so. Plus, and this is a BIG lesson learned from me, make one change at a time and ride the bike for a few rides with those changes. Also, check the plug after each ride. And, note if you were doing wide open stuff and/or tight stuff without much full throttle. If your bike is running OK but the plug is white white white and the header is a pretty blue color, you know you've been running lean and you need to start richening out your jetting A LITTLE AT A TIME. If your plug is black, you've gone too far (although you'll probably foul the plug too). If you are going to error, error slightly on the side of lean.

I would hate to see someone make a bunch of jetting changes all at once that worked well for someone else, then end up having the jetting blues I have had. These bikes are all a little different. And we all ride at different altitudes with different humidity and temperature over different terrain, etc etc etc.

One of my riding buddies here in Colorado has had little trouble with fouled plugs with the stock WR jetting. And he rides the same high altitude stuff I do. But, I had to drop my clip and my pilot for high country stuff. It could be differences in the bike, our riding style, or who knows what else. I'll never know for sure.

Also, don't think that just because you remove the air box and baffle that you have to richen all jets by 2 steps. That's asking for trouble.

Another thing: I see many of the Colorado dealers making the same mistake I made when my bike was new. They think to jet the bike for high altitude riding, you just drop the main to about a 160. One dealer even told me a 155! The jetting has to be addressed as a whole. Unfortunately, most of them don't ride this bike and they really don't know.

Am I an expert on jetting? HELL NO! ! ! ! But, I am an expert on fouling plugs! For a while I thought I'd have to start buying new ones by the case. I haven't fouled one since late last summer.

Just my three cents worth (inflation you know).


[This message has been edited by Bryan (edited 04-02-2000).]

Thanks for the reply, Bryan. I made the mistake of not checking my plug 20 miles ago. It surpised me how fast these plugs foul-just as bad as a two-stroke!

No big deal I guess, I am close on my jetting now and will do a series of plug tests to confirm before this happens again. I just ordered 5 of them-hopefully that should do it!

Ahh, the trails and tribulations of owning a new race bike!!

Well Im back at home on leave in New Mexico from Iceland now . Promised I would send in my jetting specs once I checked my notes. 158 main, 42 pilot, clip second from top on stock needle, 2 turns out on fuel screw. Altitude 4,300 feet to 9,300 feet. This is on my 99 WR400F. It never fouls plugs now and always fires up first kick. In fact, after sitting six months (drained of course) I filled it up, primed the motor with one twist of the throttle and it fired first kick. My wife is my witness!!! Oh yeah, YZ timed, no airbox lid and no exhaust baffle. It rips!!


Dude, you seem to be set up awfully, awfully, awfully lean for that altitude. Especially for YZ timing.

You are no where near the setups of us CO boys who ride around the same altitues. I have a feeling clark is going to drop his beer when he reads your setup.

Just for example, I am YZ timed and have the following setup, 48 pilot, 175 main, DVN needle with clip at #4 and 1 3/4 out on fuel screw. I also am not fouling plugs.

I'm not arguing your setup or that you not fouling plugs. I'm just amazed that we have such a discrepancy in jetting for the same altitude.

The New Mexico 5000 foot air must be way thinner than the CO 5000 foot air :D


Dougie, '99 WR400

Mods: YZ timing, Race Tech Suspension, FMF PC IV, FMF Hi FLo Moto, YZ seat, IMS 3.3 tank, One Industries Graphics

Hey Vincent.

Iceland? BBBBBBBRRRRRRRRRRRRRRRRRRR! Makes Colorado seem like the Bahamas eh?

I agree with Dougie Doug the rap star. I run your jetting when I go up to 13000 or 14000 feet.

Going a little richer on your main gives you more power up high and that's a good thing.

When I ride Denver or a little higher (6000 to 9500 feet), I run a 42 pilot, 2nd clip and 165 main. But, others I know still run a 45 pilot and 168 main at this altitude successfully.

When I ride WR timed down in Moab (4000 to 5000 feet), I run a 45 pilot, 3rd clip, and 168 main. I've yet to foul a plug with that setup. However, if I go any richer I do foul plugs.

When I ride higher than about 9500 or 1000 feet, I run a 42 pilot, 2nd clip and 162 main.

I always ride with no baffle in the stock muffler and the entire air box top removed.


I'm also in New Mexico have a 426 and while I know it is different than the WR I changed over to Stroker's recommendation of a 48 pilot and a 165 main with the fuel screw 2 out. Stock was a 162 main and 42 pilot. The stock setting wasn't too bad but was a bit lean on the bottom and would pop on deceleration. The new settings seem to be working just right. Anyway just thought I'd let you guys know that Stroker's recommendations have worked for me and they also have the WR specs. One other note, if you run at low speeds for any length of time, don't forget that your plug may look black even if your jetting is on.

Ok guys..Im baffled by your jetting advice. If Im at a higher altitude (less air) and my base line main jet was 168 stock, why on earth would I want to richen the bike? It was already jetted at sea level specs from the factory. Im certainly not going to make it richer than stock! When I got it with stock jetting and fuel screw settings, it ran ok at 4,300 feet. It started terribly though. I cured that by going out to two turns on the fuel screw. It always starts on the first kick now. It would hint at fouling plugs as I climbed altitude toward 9,300 feet. This as you know is a scary proposition as changing a plug on a WR is no easy task. I did a plug check with the 168 main jet and it was sooty black with all the YZ timing, etc... That is too rich. So I whipped out my handy dandy KTM jetting guide that a crusty old enduro rider/desert racer in the local area gave me. It is a graduated scale that uses your base line jetting specs and multiplies them against variables such as altitude and air temperature. When I do this on my chart using 168 main and 45 pilot as base lines then factor altitude and temp, I come up with a multiple of .92 or .93 which ends up being actually a little less than 158 on the main and right at 42 on the pilot. My bike does not even hint at being too lean even when ridden wide open at long stretches at a time. It has excellent response times, no lag and doesnt run hot as it would tend to if it were too lean. I just rode it over 60 miles of trails today at all altitudes and not one hint of any drawbacks. So...is it the different temps or are you guys maybe running too rich still? You can run rich and still not foul plugs on thumpers. Ive ridden them for years and my TT's always ran a bit rich. The thing you do want to watch out for is being rich to the point of washing oil from your cylinder wall with excess unspent fuel. I used this chart to jet my KX 500 over the years too with the same results. If your at all familiar with KX 500's you'll know they are plug fouling, hard to jet beasts, especially at varying altitudes. I dont know guys..enlighten me to your ways of thinking here. This thing is running way too good to start messing with again unless you have a really convincing argument.

Vincent, your card intrigues me. However, I subscribe to book of Clark. Take a look at his high altitude jetting tips in the tech section and see what you think. All I know is both Bryan and I had all kinds of plug problems when we were running the lower mains. Once I started listening to Clark's advice, my problems seemed to disappear. But hey, if it is working for you, why change.


Dougie, '99 WR400

Mods: YZ timing, Race Tech Suspension, FMF PC IV, FMF Hi FLo Moto, YZ seat, IMS 3.3 tank, One Industries Graphics

Hey Dougie, I'm really curious now if Im missing some hidden performance. I sure dont think so as my scoot seems to rev to the moon now. It seems odd that you can get away with such rich settings when Im not. I dont have my scanner with me now or Id try and scan the chart and share it with you guys, it really makes jetting a no brainer. Like I said previously, the bike did try to foul a plug at stock jetting before but doesnt even hint at it now. I never have fouled one yet in fact. What sort of air temps are you running in? I know the cooler the air the more dense it becomes and requires much richer jetting. I always take that factor into account as well. Im going to look at Clarks jetting tips and see what he's said previously. Im intrigued.

Well gentlemen, I dont mean to run this subject into the ground but... My curiousity got the best of me. I had to go and do a plug check on my bike today. As I stated, I went for a long ride in the mountains and lowlands yesterday so I was curious to see if I had a white electrode from runing too lean. Nope, its a perfect tan color all the way up and down the electrode insulator. I had been all up and down the power band just prior to shutting it off so I know its a pretty good indicator on the plug at this time. What gives guys? Are you running rich? Whats your ambient temps like right now?

Vincent & others,

I've got an excel spreadsheet that calcs the size of the pilot and main jets. It works the same way your chart does. Just enter the elevation, temp, and base jet sizes. Works like a champ.

Anyone interested in obtaining this spreadsheet can e-mail me at ron@surfcity.org and I will be happy to e-mail it back at ya.

Vincent, You are YZ timed, am I correct? When you say stock needle, is it the stock WR or YZ needle you are using? If you do get a chance, please scan you card for us.


Dougie, '99 WR400

Mods: YZ timing, Race Tech Suspension, FMF PC IV, FMF Hi FLo Moto, YZ seat, IMS 3.3 tank, One Industries Graphics

Dougie, yes its the stock WR needle in my carb. The manual stated it should be on the fourth notch from the factory but it wasnt. It was set at the 3rd notch from the factory. I dropped it one to compensate for a blubbery response on the first part of the throttle opening. It seems to be much crisper this way. Im also running YZ timing, no baffle, no airbox lid and using the stock pipe. I'll scan that card and share it with you guys when I get back to my other computer and scanner in Iceland. I'm also curious to see that previously mentioned spread sheet on jetting specs. Charts like this make it so much easier to compensate for the drastic altitude and temp changes that we have to contend with. Kawasaki used to put the same type chart in their KX owners manuals, Im not sure if they still do. All the specs in it were at least one step richer though on their chart. I strongly suspect that they did this for the liability issues of two stroke jetting. We all know what happens if you go too lean on a two stroke (at least at wide open throttle)...insta-seize! This KTM chart has always seemed just about right for me.

[This message has been edited by Vincent (edited 04-05-2000).]

Vincent- Sounds like KTM and KX two-strokes guide you have doesn't apply. 2-smokes have an ideal air-to-fuel ratio of appx 12.5:1. Four strokes use 14:1. Basically the mixture is really about the same, however the difference is due to the oil (less combustible fuel) addition and inhernet 2-stroke characteristics that are slight, but evident.

I bet your jetting is very close. The plug sounds great! You many want to try a 1 larger size main for 1 good ride to feel for performance increases, then check the plug after and compare color.

It does sound really odd that others are way richer for similar conditions--maybe everyone should do a nice plug test. It seems doubtful bike to bike differences would make such a difference. I can post a detailed account of how to do this if anyone wants it. I'm doing it (again) in a few days myself!

The WR comes lean from the factory. So consider stock settings as lean already at sea level.

Would like to see the chart and spreadsheet.

Bryan, if you can post this chart this may help everyone. Just be sure it is 14:1 ratio...Rich and Clark, can you confirm 14:1?

You guys are fun to listen to--

I can explain it all but it gets very complicated.

1) The stock main jet was chosen as a compromise for the cork in the exhaust. Forget the charts because it was too lean as soon as you uncorked it. Follow Clark's advice for the main, he is methodical and has tested. Keep in mind main jets are for full throttle only. As such, your plug readings are in question.

2) Mid-range : look at the needle code, nobody seems to be talking about it. The second letter is critical to clip position. A DTM#2 EQUALS a DVP#3 above 1/8 throttle. I suspect everyone is very close in the 1/8 to 3/4 throttle range. No surprise here...

3) Low-Throttle : If you have a DTM needle the straight diameter is 2.715mm and normally would be too rich at high altitude. To compensate for this a 42 pilot is a viable option. Others such as Clark have gone to a leaner DVP with a 2.735mm diameter and a 45 or 48 pilot. The straight diameter only effects 0-1/8 throttle, not above.

Am I right? was the needle a DTM?

Thats my guess---

James Dean

-james dean- great job on the needle decode. im going to keep a copy of that. 1 thing to wonder about is the wr main jet. im not sure it is lean for the cork because as stock the throttle stop prevents bike from ever running on it.


You're probably right that the bike may not even need a main jet at all with the throttle stop in place. Especially with a small taper needle such as the "D" (3/4 degrees). Small taper needles transition to the main at higher throttle positions. Keihin accomodates this in OEM conversion charts with a special note at the bottom to adjust the main down 2 sizes using triple taper needles.

I think Yamaha had several considerations when picking the main jet. Putting the baffle in and out and the EPA are probably the big factors. The baffle is so convenient to remove, unlike the throttle stop, it looks like it was part of their overall plan for the users. We can only guess.

James Dean

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