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fisher

2000 WR - FINALLY runs great

8 posts in this topic

It's been a long two months since I purchased my new WR 400, but I finally have it running strong. . . everywhere throughout the throttle range. From the first time I brought the bike home, it never has ran right until last Sunday (10/1/2000). To make a long story short, this is what I have done: (hopefully this will help somebody in need!)

WR Timing, No Baffle, No Airbox Lid, No throttle stop (trimmed)

MAIN: 172 PILOT: 45 AIR SCREW 1 1/2

ALTITUDE: 0-1000 TEMP: 75 F HUMIDITY: 50%

I started out by changing all of the above settings/parts on the bike. This helped quite a bit by not letting the engine run too lean, but I still had a considerable problem with a bobble/hesitation/stumble in the low to mid range. To fix that I did this (of course from help from people on this message board):

I changed the jet needle from the stock DRS (which I think is trash) to a DTM. Somebody please correct me if I am wrong, but I think the DTM needle is a stock 1998-99 WR 400 needle. Regardless of what it is, get a DTM.

This fixed the low-mid stumble/hesitation problem, but I still had a small hesitation a very minimal throttle opening. Every time I went from zero to 1/8 (probably just 1/16) throttle the engine would stumble. It would recover shortly but I couldn't get it to change by adjusting clip positions, pilot jets, or air screw settings. :D Here is what I did to fix that:

Make an adjustment to the accelerator pump linkage. (behind a black cover on right side of carburator) Mine was set so that as soon as I barely touched the throttle, the accelerator pump squirted gas. This was causing a rich condition at that extremely small throttle opening, which caused the stumble. You can screw the adjustment screw IN (a little bit)so that the accelerator pump is delayed before it squirts the fuel when you open the throttle. Did you get that? I barely did. This will also help people that are having trouble with a stumble after a fast throttle opening. You will still have to tailor your jetting to the area/climate in which you ride. Good Luck!!

I hope this helps somebody who is having trouble with their 2000 WR. Thank you to everyone that has helped me on this site. :)

Sean Fisher

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Sean,

How much did you turn the screw IN to get this VERY low throttle hesitation to stop?

What you're saying is that it was delivering too much fuel. Also, what clip position was the DTM set at?

The DTM is .05mm richer at 0-1/4 throttle than DRS (last letter - MNPQRS). This is a big change richer. An intermediate step would have been to go to a DVP needle, .03mm richer. This is described in the tech section by Clark. Either way it looks like you have a good fix.

Hick and I have been looking at the pump adjustment screw and would like to know the range where it needs to stay within. This is a very sensitive adjustment and the more inputs the better. If it pumps before 1/8 throttle, it may put fuel on the face of the slide.

James

[This message has been edited by James Dean (edited 10-03-2000).]

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James, What post has the break down of needle specs? The one that tells how to 'read' the part number?

I tried to find it & I guess I just plain missed it.

Brian

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Just brought it back to the top, "YZ426 Jetting Boosts YZ/WR400 Midrange Power" and updated the first post with more detail on codes.

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I just rejetted today 172MJ,45PJ and left the DRS in its stock position. 0-1000ft and I think this is fine. Its funny because after rejetting I saw this post. It doesn't bog in whoops anymore. Some bright parts man gave me a Mikuni MJ had to run back. Will the needle change do as much as the other 2 jets?

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Tree Crippler,

The improvement will not be as noticeable as your changes up to this point. They will be an improvement though. The change in jetting from the needle swap will be near 0-1/4 throttle going from DRS to DVP to DTM. I would suggest going to DVP before DTM as was described above. See Clark's tips in the tech section on jetting.

Be aware that the middle letter is relative clip height and affects midrange 1/4-3/4 throttle. The DR- is one clip richer than DT- which is one clip richer than DV-. Therefore, DRS#3=DTM#4=DVP#5 between 1/4 and 3/4 throttle. If you have been using DRS#3 then probably try DVP#4 or #5. Then maybe DTM#4.

James Dean

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Originally posted by James Dean:

Sean,

How much did you turn the screw IN to get this VERY low throttle hesitation to stop?

What you're saying is that it was delivering too much fuel. Also, what clip position was the DTM set at?

The DTM is .05mm richer at 0-1/4 throttle than DRS (last letter - MNPQRS). This is a big change richer. An intermediate step would have been to go to a DVP needle, .03mm richer. This is described in the tech section by Clark. Either way it looks like you have a good fix.

Hick and I have been looking at the pump adjustment screw and would like to know the range where it needs to stay within. This is a very sensitive adjustment and the more inputs the better. If it pumps before 1/8 throttle, it may put fuel on the face of the slide.

James

[This message has been edited by James Dean (edited 10-03-2000).]

James,

I see what you are saying about DRS to DTM being a real big jump. The main reason I went to this jet was that many of the jetting examples for the 2000 WR have a DTM. As far as the Accel. Pump adjustment, I screwed IN the screw just until the low,low end hesitation stopped. If you have to screw it in a turn or two, then back it out until you are at the threshold of hesitation. My gut feeling is that you don't want to be screwing this in too far. This is just what I think, I believe you probably know more than I do.

SEAN FISHER

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Thanks James, I'm glad your not tired of answering our questions yet. It seams the dealers around here think the only jet you ever have to change is the MainJet. I race Enduro's and Hare Scrambles in the NEast so jetting is always important. Already got good results in a H/S on a front flat. Hope the new WR holds up for its first Enduro. Might wait till next year.

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