Wanted: patient people to help me with my 2k WR

The bike is idling pretty well and running pretty strong but a sudden blip of the throttle gets hesitation and there is some backfiring on decel.

-Richen up the bottom end. Back out the fuel screw one more turn. If is still hesitates/bogs you could try a step richer pilot and see if it helps.

Steve, Glad to see things are going in the right direction. Many other guys will disagree with me on this but if I were you I would put my Carb back to stock with stock jets and see how it runs. From your name it sounds like you're in Arizona, with the bikes stock jetting your bike should run pretty good. Between my father and I we have owned 6 WRs, all have started and ran great with stock jetting. Some people make small minor changes to get their bikes to run at their peak but for the most part stock jetting is where it's at. I can't remember you stating that you bought the bike brand new or used. If it's used, you deal with whatever the previous owner did to it. If you took the slide out of the carb make sure that the "slide plate" in on correctly (just the opposite than what common sence would make you think). I've used carb cleaner numerous times with great results, that coupled with some compressed air you should be able to get everything clean, their are a lot little components and passages on these carbs, take everything apart and clean it and replace everything with stock specs...

Cutting the throttle stop too much is definatly a problem, buying a YZF throttle stop is the way to go, they're just a couple of bucks and you get a lot of piece of mind by having it. It sounds like you have a lot of plans with your bike to make it rip, personaly I would get it running great first then start to mess with other mods..

Best of luck, Dan :)

Between my father and I we have owned 6 WRs, all have started and ran great with stock jetting.

True but they run better with a YZ needle.

IMO. :)

So what is the difference between a YZ and WR needle? The taper? What year YZ has the best needle? Don't they change it all the time? My bike runs great with the factory jetting and the BK mod but I am getting ready to do the 450 cam swap so a YZ needle couldn't hurt!

So what is the difference between a YZ and WR needle? The taper? What year YZ has the best needle? Don't they change it all the time?

Yes. YZ has an E taper, WR has a D taper.

As far as the YZ 426 is concerned avoid the stock '00 needle, '01 and '02 were the same.

My opinion on this it is an easy thing to do mechanically and is less than fifteen bucks, but it makes a huge difference. Changing the taper is much more radical of a change than moving the clip position, for example. If you don't like it or can't get it dialed (you may need a smaller main depending on your situation) you can easily go back to the WR needle.

Yamaha PN for an '01 YZF 426 needle:  5JG-14916-JP-00

It is an OBEJP. Stock position is (as usual) right in the middle.

EKP, 1/2 clip leaner for fine tuning the clip pos.: 5JG-14916-EP-00

(Attn. parts counter dude: latter PN is off the '00 fiche).

True but they run better with a YZ needle.

In what way?

My bike doesn't stall or sputter.. I've tried to make it backfire and it won't... Nothing but clean brutal power with totally stock jetting..

In what way?

They pull harder when you come on to the taper, particularly over 1/2 throttle. The affect below 1/2 throttle is less noticeable, and it probably has little or no affect below 1/4 throttle and none at idle, so any backfiring or immediate throttle response won't change, it just pulls harder as you wind it up. I can see where a guy may prefer the way the stock needle works, I am just not one of those guys.

If you just think about the contraptions they hang on the WR engine-wise don't you wonder how the jetting could possibly cope with that? I'm sure if I had a WR 450 the first thing I'd try, jetting-wise, is a YZ needle, but I've no experience w/ the newer blue bikes, so keep in mind I'm talking about the 426 only (back when the airbox was still the same, this could have a very significant affect on the jetting WR vs. YZ 450).

You may need to rejet other circuits, particularly the main, when you change tapers, if not the bike could conceivably run worse, but this isn't very likely unless your jetting is really off to begin with.

The reason I've come to this fervent belief is because I ride at altitude and at one time I had four riding buddies w/ WR 426s. Around here nothing runs its best w/ stock jetting, I got promoted head tinkerer and rejetted all the WRs about the same time I discovered TTalk and James Dean. He was a fan of the E taper in the WR so I tried it and was very impressed w/ the results.

Anyway, as far as engine changes WR vs YZ 426, in order of affect on, or significance to, performance I'd rank them like this from biggest change to smallest:

- Throttle stop (duh)

- Exhaust insert

- (tie) Airbox lid, YZ taper needle, exhaust cam timing

- Air Cut Valve

Just my take on this thing. I'm the resident rabid E-Taper evangelist seeking to convert all nonbelievers. :)

Well, thus far I've gone from the 165/42 to the 170/45 as recommended with the pilot screw at 2 turns. WOW! What a difference, throttle response is excellent, and the bogging is gone. The only thing I noticed was that there was a slight lope at low rpms and that unless I'm above 60mph (judging by the cars I was passing on the rode parallel to the trail I was on) in 5th it feels as though I'm bogging a little. Still have a few mods left but not sure I want to add them yet. I'm going to have to play with tires and tire pressures because I was spinin something aweful all day.

BTW, I don't remember who suggested the exhaust spacers for the 85 but it did help. I don't think any further mods will be necessary until he's ready for more power :) THANKS!

Dan, you're right, the bike ran well before but I''ve opened up the airbox and piped it. Seems to me this thing pulls harder than it ever did before, especially at the bottom end. Thanks for the input. And now there is no low end bogg, couldn't say that before.


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