01 wr 426 Part #'s

I want to order the yz throttle stop, and if they make a gytr exhaust insert, one of those. I want a throatier exhaust for the trails, and use the vortip for street riding. Nobody Seems to be able to know what I'm talking about (The Idiot yamaha dealers around here). I'm still waiting for my baja designs catalog too :) I really need these part #'s so I can get this stuff ordered. Can someone post a tech article on the throttle stop for me, I want to do that and the bk mod together.

My british only catalog hasn't come yet for the bsa either :D

Trt trail rider, didn't it say you have a gytr insert in your stock exhaust? My bike has a 165 main jet in it right now, does the grey wire really do anything? The light blue wire did help,thanks guys I trust your advice. What is the proper length that the stock throttle stop can be gound down to? What tires does everyone here run for sandier trails, but will still hold up in harder terrain, and some street riding? I was gonna order some dunlop 756's.

I have 120 miles on the bike now. Is it to early to uncork it, or will I be ok? Is this thing going to be ALOT faster? I sure hope so :D


I cut the original throttle stop on my WR's to 23mm. I measured from one end of the bolt to the other end and cut it with a pair of wire pliers. They look like lineman's pliers but are for tying steel on rebar of swimming pools. I also disconnected the grey wire from the connector and insulated it with silicone and a wire nut. Look for the grey wire paired with a black wire with a white stripe coming out of the ignition box. If I remember correctly its the only single pair wire coming out of the CDI.

The 739's that came with your bike aren't bad tires, they'll last for a long time in any soil but are made for hard terrain riding. If you ride in a fluffy soil you'll need to lower the air pressure to get them to bite, otherwise get ready to plow often. I've ridden one of my bikes to almost 1500 miles on the original tires, alot of it was hard dirt roads and some street riding and they still look reasonably well. I believe they're a really good tires for a guy who's willing to give up some traction for a long lasting tire that will put up with alot of abuse. If you plan on racing get a soft terrain tire and a YZ tank and seat.

Lose your airbox lid, or at least the snorkel and the exhaust insert so your bike can breathe. You'll be shocked how much more power you'll enjoy with just the throttle stop and the baffle removal.

My bikes had alot of popping on letting off the gas after doing these mods but some other guys didn't experience this. I guess its altitude, humidity, and temperature that may be the difference.

I'd say at a hundred miles its time to change the oil, do your free mods and let her rip.

I've never had any bogging so I haven't yet done the BK mod, but many of the members here swear by it and the E needle jetting. All I found was that the bikes started easier and carborated better (virtually no popping) after doing this.I'm sure you'll notice the difference after performing these mods.

Thanks husky rider, I did the 100 mile oil change already. There was a lot of junk in the filter. Got any pics of your old huskies?

Can someone please tell me these parts numbers though?

E needle jetting? :)

E needle jetting?

An E series needle, as I understand it, has a slimmer midsection. It takes up less space down the center and will allow more fuel to pass through the mainjet.

I believe the stock needles are DRR for the WR, and EJP for the YZ.

I've read several posts about how the letters designate leaner or richer but have yet to absorb it between my ears.

I went to stock YZ jetting to compliment the YZ timing mod I did to the bikes. I figured this would be a good starting point for where I ride, i.e. sea level, average humidity and temperatures.

I've read that alot of guys have had great results with leaner jetting and smaller main jets.

I experienced noticeable popping on letting off the throttle after doing the free mods (grey wire,throttle stop,baffle and airbox cover removal) so I went to YZ specs which ??are richer?? This almost eliminated the popping and made starting without the hot start much easier.

I'd consider myself an average rider and a below average mechanic on anything other than routine maintenance so I'd rather not go to lean and take a chance on damaging an engine. I'd probably go to an EKN or an EMM if I had someone to assist me in the jetting process and help me fine tune it. There are variables to consider when jumping up and down in sizes and correlations between different circuits of the carburetor which I still am not up to speed on.

I was totally happy with the performance of the bikes after free mods but didn't like the popping or the hot starting.

I hope this helps you.

If you want to learn more about the jetting there are a bunch of threads in here that can enlighten you. I hope you can absorb more than I did reading them.

Have fun with your new toy, Kelly

1) YZ Throttle stop PN: 5JG-14591-00-00

2) YZ Needle (EJP):  5JG-14916-JP-00

YES, uncorking/uncovering/unstopping your bike will make it much faster. At that point you need to try YZ jetting (mainly just a needle change).

756 tires are pretty good in sand. 773 is better but hard pack eats it up pretty quick.

An E series needle, as I understand it, has a slimmer midsection. It takes up less space down the center and will allow more fuel to pass through the mainjet.

Close enough I suppose. The first letter designates needle taper, or the angle of the taper. The E has "more" taper, meaning the transition from fat to skinny is steeper.

I've read several posts about how the letters designate leaner or richer but have yet to absorb it between my ears.

Then one more time won't hurt. Three letters in the needle code represent three different dimensions, in the following order:


Clip Position

Straight Diameter

Taper governs the rate of transition from just over idle to just before WOT. IMO it is a mistake to simply say "leaner" or "richer" taper because that oversimplifies what changing this aspect does. It is a pretty significant change.

Clip position is self-explanatory. Each two letter change equals a full clip position (note that letters O and I aren't used), so an EKP is identical to an EJP, it is just 1/2 clip leaner on each setting...

The last letter indicates the diameter of the needle on the straight portion, which governs jetting before the needle "comes onto the taper." So an EKQ is one size leaner just off the pilot compared to a stock YZ EJP needle.

See the chart:


Thanks for the chart and the heads up.

I can't believe how lean my WR needle was compared to the YZ. No wonder it was popping all the time.

I guess I shouldn't worry about damaging the engine with the EKN or EMM. I hope running the original needle for a year didn't hurt my bikes.

One of these days I'm gonna play around with the jetting to try and fine tune it. My bikes seemed to like the DRR more at the top end and the EJP on the low end, now it seems snappier in the low revs and only fair on top. I suppose this is where using a smaller main helps.

Guys like you and others are what keep me coming back to this site to pick up little bits of usefull info.

Thanks, Kelly

...now it seems snappier in the low revs and only fair on top.

Pure speculation on my part, but it could just be a case of perception. With the sleepy WR transition from off to "on the taper," it may just seem like you're losing out up top.

I only say this because I always had the benefit of riding my YZ back to back w/ two friends' WRs while I was sorting out their jetting. Pretty soon I figured out the only sorting I needed to do was to just copy what I had on the YZ onto their WRs. In short I didn't notice any loss of rev-out with the YZ needle change in the WRs. Also, it seemed that, as far as the main jet circuit went, the different exhausts (PC, WB, Uncorked WR, stock YZ) had little if any affect on main circuit jetting.

Hope this helps.

Thanks guys, will be printing out this page shortly :)!

What is your view on the bk mod? Is it worth all the work involved? The only time I notice a tendency to stall is really slow and slick corners, I keep trying to blip the throttle to keep her from stalling out. If the bk takes away the lag when doing this, I'm sold. And its between .3 and .5 seconds right? I know I'm not supposed to open and close the throttle like an idiot too, and I don't. It's just kinda hard to explain. :D

Any exhaust tip recommendations. I'm torn between gytr, motobillet, and the vortip. Motobillet is the cheapest. The 450 and 426 have the same muffler? I want the tip that flows the best.

What is your view on the bk mod?

Any exhaust tip recommendations?

Bk Mod

For the ’01 model the BK is still a big help IMO. It is not a lot of work to complete this mod, it is a very, very simple operation. You just need to have a good tap, compatible screw, some kind of spring, and be willing to drill a hole in an $800 part. It is all mental, as they say. I say do it if you rate your mechanical ability as above screwing in a light bulb but perhaps below changing the brakes on your car.

Bottom line is I don’t want you to put up with marginal response out of such a great bike. In a few minutes I, or any number of other TTalk members, could have your bike jetted perfectly (or acceptably close) and delivering crisp response. Once you get that, see how easy it was and how great it feels, you will mourn the days that you rode and lived without it. I think the 426 really benefits from a little carb set up, particularly the ’00 and ’01 years.

On the squirt, I may be the only one that thinks this, but I always thought trying to accurately time the squirt was silly and that simply measuring the stroke was easier. Do the mod, measure the stroke, reinstall the carb (leave stop watch in its drawer). I believe stock is about 3 mm of stroke at the actuating rod, between 1 and 1.5 works very well. There is also a factory adjustment screw for the pump timing located just under the slide pulley. After you do the mod you may try turning this screw in (clockwise) 1/8 or ¼ turn to place the now shorter stream of fuel from the pump a bit later in the throttle movement. This isn’t always an improvement, but is a very simple adjustment that can be done with the carb still on the bike.


The stock exhaust is very good, I’m not sure I can comfortably say that any aftermarket replacement or modification is an improvement unless:

1) You need a spark arrestor

2) You need to meet a Db requirement

Hope this helps.

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