DRZ400 has same carb as WR426... best fix?

9 replies to this topic
  • ballistic

Posted June 05, 2001 - 07:07 PM


Just to compare notes, what would you guys suggest as the best setup for these carbs, considering its the same 39mm Keihin TPS carb?. I notice with interest that the carb discussions on this forum are alot more advanced for some reason. Something to do with that James Dean guy? Is he a carb engineer or something?

Many of us over on the DRZ forum are finding a just off-idle cough or hesitation. I have the following setup which is pretty typical for many DRZ's:

-airboxlid gone
-twinnair filter
-aftermarket pipe
-strokerspeed.com smog removal kit with following recommended setup: clip in middle postion, 2- 2.5 turns on screw, install the included #100, #48, #172 jets (sorry i dont know thier proper names). And the long big needle (name?).

Some run a #165 or 168 or 170, even 175 but the consensus seems to be 175 is too rich. Maybe the #168 is a good average? Some use the #50 instead of the #48. Whatever.

After I rejetted with the smog kit it runs better, more power, faster, but the slight bog is ruining all my fun.

From what you know, and it sounds like some of you are doing all kinds of things to your carbs, whats your best guess? Aside from WR's being higher revving, and the 426 having more displacement, should not the carb setup be analogous(sp)?
Any thoughts appreciated!

  • mcarp

Posted June 06, 2001 - 03:51 AM


Hi Ballistic-

Well, the carb on the WR and YZ is NOT exactly the same ('00 and '01 models). The FCR2 model is on the Yamaha, and will never see the DRZ.

Yes, jetting should be close, but certainly you can't use the same for both models.

The slight hiccup is there on the WR as well. However, there are ways to eliminate it.

First, turn the idle up a bit. Perhaps 200 rpms faster than normal. This combined with a 48 PJ and #100 main air jet (the same the YZ runs, the WR runs #75 stock) made my WR have no hesitation, except when cold. If may buck and stall during the first few minutes of riding, but that's normal.

The idle speed really made the biggest difference.

I don't believe James is a carb engineer, just a serious hobbyist. You'll find the guys that ride WR's demand the upmost performance, and often we go to gret lengths to get that extra edge, whether it's racing or just plain fun.

Another item that COULD be the problem (don't know for sure) is the TPS. Perhaps it is out of adjustment slightly? One more thing to look for is to avoid over-oiling the airfilter. The WR is touchy with this- in fact you have to wait a day after oiling before install or it will bog and potentially foul plugs (mine does anyway)

As a WR owner, I have to roll on the gas--just wacking it open will make it die if Im chugging along at low rpms.

Hope that helps--try the idle thing and let us know what happens. The 50PJ may make the bike more prone to stalling. Careful pilot screw adjustment is key as well.

Good luck,

  • z4me

Posted June 06, 2001 - 06:26 AM


Originally posted by mcarp:
Hi Ballistic-
...The FCR2 model is on the Yamaha, and will never see the DRZ...

Untrue. The DRZ has the FCR2 - the main difference being the throttle position sensor.

- Sean

  • mcarp

Posted June 06, 2001 - 06:59 AM



No kidding????? I could swear the FCR2 was developed to be used only on the WR/YZ for Yamaha. If not, my mistake... Is there NOT a TPS on the DR?

Regardless, I would try to raise the idle a little before doing anything else. It helps on the WR's at least. YMMV

  • z4me

Posted June 06, 2001 - 07:40 AM


I have the S model. I was considering upgrading the CV carb on it to the FCR but was told that I what I really wanted was the FCR2 from the dirt-only models. They said the original FCR did not have the TPS on it.

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  • James_Dean

Posted June 06, 2001 - 08:08 AM



I am just another enthusiast interested in getting the most performance from my bikes with jetting and also happen to be an engineer. The same jetting tips will work on the DRZ. A smaller main jet is usually used on the DRZ than the WR. Try an EKP needle in clip #3, Yamaha P/N 5JG-14916-EP.


The '98 and '99 Yamahas have a different version of FCR carb than the '00 and '01 Yamahas. They share many of the same components. The newer version, often called the FCR2, is easily indentified by the hot start button built into the body of the carb and no hoses.


  • ballistic

Posted June 06, 2001 - 08:24 AM


What effect in general will an EKP needle have over the DVR needle (how will it differ?)
DVR in #4 from top is what I have now.
Thanks in advance.

  • James_Dean

Posted June 06, 2001 - 08:52 AM



The majority of the gains are in the mid-range throttle position, 3/8-3/4 throttle. The front lifts up easier. This is the "standard" taper needle for the FCR carb whereas the DVR is less than standard taper and is made to run lean in the mid-range.

The reason for the smaller main is that the DVR is thicker at the tip and partialy restricts fuel at WOT. The EKP is not as thick at the tip so will flow more fuel unless the main jet is reduced to about a #158-#165 on the DRZ (as an estimate). I had a generous person send dyno results showing #158 was best on a DRZ with Yosh Ti Race exhaust using EKP#3.


  • ballistic

Posted June 06, 2001 - 09:11 PM


Stroker speed told me that by removing the "coast enrichner" smog crap, the carb is made lean and that is why they ship the kit with a #172. Many are skeptical of that theory however, and opt to use #165 "against Strokers advice". Does that make any sense? Alot of confusion and possible bad advice has been disseminated pertaining to DRZ carberation. I like the sound of things being said in this forum better, it seems you guys have done some actual testing and refining.

Do WRs have the smog octopus? If so, does removal impact jetting?

  • James_Dean

Posted June 06, 2001 - 11:14 AM


Some of us have done LOTS of testing.

Only the '98 and '99 Yahaha WR400s have the "octopus" with all the hoses, newer Yamaha models do not. In the TTalk technical section Clark Mason did a write-up on removing it from the '99. I couldn't speculate the extent it changes jetting. There are enough variations in altitude, temperature and exhausts that you just about have to set the main jet for your own conditions and ability. To give you a range, the stock YZ426F main is #162 and the YZ250F is #175, both use E taper needles.

I have received positive results back from most riders using the EKN or EKP needles in the WR400, WR426, YZ400, DRZ400, KTM400, and KTM520. These are with AND without the octopus. The results that stand out are that the stock 520EXC will not rev with a #168 main jet while using the EKN (#160-162 best). The DRZ appears to have a similar situation. There is great potential for the DRZ if someone wants to take the time to experiment.



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