Move Clip Position or Richer Taper Needle

I've been working on eliminating the exhaust popping on my 00 YZ426 during deceleration. I opened the pilot jet screw from 1 & 3/4 to 2 & 1/4 and the popping no longer occurs at very low deceleration speeds.

Now when I am running at high speed and I chop the throttle I don't get the popping right away, instead it will occur in the middle speed range. I assume this is caused my my jet needle being too lean. I purchased the 01 modle jet needle some time back per the recommendations from this board and DRN, but I haven't installed it yet. The only differene in the 01 needle is the taper diameter makes it a richer needle than the 00.

I looking on recommendations on what to try next. Should I lower the clip on my 00 needle to make it richer, or should I just install the 01 needle at the stock position since it is a richer needle ?? Which will make more difference ?

I don’t think the clip position will affect closed throttle jetting at all. I would try the ’01 needle which is richer on the straight diameter (taper is unchanged) first unless you are at higher elevations, the ’00 needle (EKR) is too lean off the pilot, but I still don’t think this will address your problem, which according to your post is closed throttle.

To really dial in closed and neutral throttle you may want to try an adjustable Pilot Air Screw, this part replaces the fixed-size stock Pilot Air Jet.

But first it sounds like you should try a richer pilot. If this cleans up mid-rev deceleration but creates a rich spot at high rpm trailing/neutral throttle settings a larger PAJ will straighten this out.

For some all around comparisons I suggest you post your elevation, current jetting and riding impressions.

Hope this helps.

Now you've done Hick, here comes the real questions !! I'm at 850 feet above sea level. In my 2000 manual the last 3 digits of the stock needle are EKR. The manual says the "E" is the taper angle, the "R" is the diameter of the straight portion. The stock 01 needle is DKR (at least this is what my local Yamaha shop told/gave me), and my manual says a "D" is richer than an "E", which means the taper angle is what is richer, correct ??

Regarless, I am confused about the Pilot Air Jet, vs a Pilot air screw. In looking at my Carburetor on the bike, I see no extenral hold to accomodate a Pilot Air Screw ?? Is this an internal part ?? If so, how would I adjust it ??

The ’01 YZ came with an EJP, not a DRR. The WRs have D** needles, I think the ’01 is a DRR, not DKR though. I have both in my garage, BTW, in addition to an ’00 YZF :)

The ’00 needle is EKQ, ’01 EJP. Q to P is two sizes richer on the straight diameter (K to J indicates a half clip richer).

At 850 ft. your bike may benefit from some richer jetting, and since you were smart enough to try and put the ’01 needle in there, a big improvement even down here at 4k ft., you are heading in the right direction.

Unfortunately, a dim bulb of a parts guy has foiled your plans. DO NOT put that D** needle in your bike. Instead, go find the dim bulb and berate him mercilessly until you get the right needle, while you are at it get a 45 and 48 pilot and a 165, 168 & even 172 main jets to try. Then go ahead and change the needle and try a richer pilot. Once that is dialed try the main jets.

I’ve gotta run, maybe somebody else in a similar elev. can help us out here, if not post a new topic about jetting @ 850 ft. to take some more of the guesswork out of this.

Okay I’m back.

The Air Screw I mentioned replaces a fixed size air jet called the Pilot Air Jet. Your YZ has a size 100 PAJ. The Air Screw installs in its place and is adjustable so it can take the place of any fixed size jet.

There is also a Main Air Jet, these air circuits apparently tend to meter jetting in conjunction w/ their respective fuel circuits at higher rpms. The idea is you select the fuel jet that makes the best power at your torque peak and then select the air jet that works in concert with that fuel jet to make the best power at higher rpms, like your hp peak.

The two air jets are located next to each other just inside the air boot, naturally, because that is where the air is :)

If you read the jetting/tuning section of your manual it mentions that you may need to change the PAJ if you change the Pilot (fuel) Jet.

Your Main Air Jet is a 200, the biggest size available. Quite a few guys, myself included, have removed this jet altogether.

Hope this helps. Meanwhile try an EJP and a bigger pilot, I think this will improve things.


you should simply lift the needle one clip. that will get rid of the back popping.

my experience is that the needle gently back pops and the pilot circuit is really heavy in comparison.


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