Another Stupid Jetting Question...

70 replies to this topic

Posted December 12, 2002 - 01:28 PM


I always blip the throttle as well...I always turn off the fuel before I shut down and let the bike run out of gas before I put it away...(Old Habit)

This past Sunday I knew for sure I was going to foul a plug. I had let my YZ sit outside all night (Chained to my trailer). When I woke at the track the outside temp was 24 deg....with Ice all over it.... I turned the petcock on, blipped the throttle a couple quick times and she fired right up and ran like a champ. Last year I used a 60 SJ for a little while and had a couple of plug issues, but since installing the 55 things have been great.

Bonzai :)

  • Taffy

Posted December 12, 2002 - 02:09 PM


that wasn't aimed at any one person-yami especially. it's just that if we start agreeing on 45/48 PJ what has really changed?


i'll never forget trying to help one well known rider who's name honestly escapes me, and asked him to tell me the way the bike started from cold? how long before it 8-stroked? stalled? came off choke? i don't think he took it seriously-just makes me smile that's all!

now i see the 55SJ works great and i think that's brillant, so well done the first guy to try it. i was just pleased to get you down to the 60SJ.

yami, what's the smallest MJ you've heard of over here coz i know that some DR boys in carolina were on 135-140MJ.


ps met my first TT member tonight. motoman42 came out for a scoff at the trough and had a great time. 8 bikers at the table! if you're all as good as him you're a good bunch.



  • R_Little

Posted December 12, 2002 - 04:23 PM


Steve, one other thing.

Are you sure the rest of yr bike is good to go?
What I mean is, are you sure it's jetting.
Usually, the temp would only make a subtle change in the way the bike runs. You know a little rich/a little lean.
If it really started to run like junk one day, maybe it's another issue.

Are you sure the air filter is clean, the exhaust pipe isn't clogged or smashed. I also read that if the wires on the coil get dirty or loose the bike will missfire all over the place. Also, before changing jets, make sure the carb is clean to begin with. All the jets in the world will not fix a dirty carb.

Just a thought.

  • Steve_WR400F_#61t

Posted December 12, 2002 - 09:13 PM


Ya, I think the rest is ok. I knew it was running too rich before anyway. Just when it was warmer, it didn't seem to matter too much to the bike. It would foul plugs every 8 to 10 rides and they were pretty black when I pulled them out. The pipe is nearly new. I got it in September and it worked wonders on power. Just felt a bit flat on top, again I think I was too rich with the jets. It was when the cooler temps hit that it started the hesitation/popping thing around 1/2 throttle. I can move this hesitation with needle position and main jet stuff. If it's not raining/snowing this weekend I plan to test some stuff out. We'll see how it's running then. Just don't think the needle will be in yet. The shops around here are really slow. If they say one week, that usually means two to three. And they said it'd be about a week before the needle & the SJ would be here.

One thing I'm gonna try this weekend too is the gas. I used to run just 91 octane pump gas. About a month before the cooler temps arrived I started adding NOS Octane Boost to the pump gas. Ran fine... until the temp change. This weekend I'm gonna try plain ole 91 without the booster additive.

  • dominator426

Posted December 12, 2002 - 11:27 PM


Yeah, hang in there, Steve...
Octane booster would make it run richer...but, as mentioned, that DRS really is too lean. EKN's thinner straight portion allows more fuel at low throttle settings, including "idle". Then, the stronger taper allows more fuel at high throttle openings which is why it uses a smaller main fuel jet. Consequently, the thinner straight portion draws more fuel, but from a smaller MFJ, creating a good balance. Uncorking, which increases air flow, created this need for more fuel, as does denser/colder air. I'm actually pretty maxed out on MFJ(178) with my DQQ, which is why I'm switching to an EKN and smaller MFJ.
When I first started uncorking and rejetting, I actually sanded down my original DQR to a DQP-1/2 and was able to choose the DQQ.
You can also give your settings a second test with air-box cover ON and note how less air (richer) affects different fuel circuits.
Also as mentioned, the smaller starter jet should give you a leaner and more user-friendly cold-starter circuit (choke). I still have stock SJ but I noticed that, during a cold start, I still get just enough extra fuel for warm up from SJ until I 1st open throttle, after pushing starter knob back in! If #55 SJ is too lean for easy initial start, a couple blips to prime it should work.
I can't avoid covering part of my rads from 50*F and lower for my engine to run at proper operating temperature, by the way...Have you done BK mod yet? How's your spark plug gap? That iridium "CR8EIX" sounds like a good plug...

  • R_Little

Posted December 13, 2002 - 05:50 AM



Sounds like yr bike is fine. Just didn't want to rule out the obvious. You know tight valves are a cause of rough running too, and since you are waiting for jets and such, ya' got time...

I ordered my needles from North County Yamaha (760)432-9501 for $8.50, They get here to NYC in 3 days. Why don't you call them and order a slightly different "E" needle like a P vs. an N. Maybe it will arrive faster.

Note your comments re fuel. In the NE they run oxegenated fuel in the winter. I guess that runs a bit leaner too, might even have more of an effect around here than the cold weather. I know my stock jetted DR650 used to ping like crazy on it till I "Dynojetted" it.


  • Steve_WR400F_#61t

Posted December 13, 2002 - 10:58 PM


Since I'm waiting on my needle and SJ, anyone know what the ACV and BK mods really do to the bike? I've been thinking about the BK mod and really considering it. Bypassing the ACV is what I'm questioning here. What's that do? Why should it be done? Etc...

  • dominator426

Posted December 13, 2002 - 11:40 PM


Disactivating the ACV by reversing the diaphragm and sealing the vaccum hole (and switching to a larger PAJ or smaller PFJ) stabilizes the pilot circuit mixture and idle.
BK mod allows you to limit accelerator pump squirt duration by installing adjustment screw, to about 0.3 to 0.75 seconds from the stock drowning 4 to over 5 seconds.
Try a search...

  • R_Little

Posted December 14, 2002 - 07:42 AM



Did some O/R riding in about 45deg and Drizzle/Wet.

Found the following:

Starts first kick like always. Settles to a nice idle after 1 minute or so. While idle used to raise as bike warmed, it's more stable now, maybe even sinks a little as bike warms. The EJN needle fattening up the idle I guess.

The off idle response with the BK is awesome. No more bog, Period. Rode with reckless abandon on the throttle and only stalled it once. Maybe I could go a little less on the AP. At .8 sec now. Pilot stock 42/75 2 turns out.

Mid range is big fun. Bike feels maybe slightly rich here, but I was riding in the rain. I get a little miss in the whoops that I don't know if I used to get. It's close with the EJN needle.

On road runs the upper end is still flat, and I'm begining to see Taffy's light. I can tell the top end power drops off as the bike warms. One my last run, I felt the top end rush come back. Then I understood why. On decel the bike started to pop. Ah, the float bowl ran dry. I needed reserve!

Okay, so I figure all I need to do is keep the mid where it is and lean out the top by a EKN needle and/or a 162/160 main. A stock 165 is in there now. What does the commitee think, EKN or smaller main? Taffy, I believe I know what you think!

While I'm waiting for JD'd jetting guide, can anyone again reconfirm the difference between a EKN and a EJN?

If this don't do it I'll give in and buy Taffy spec'ed air jets and change everything!

Steve, DO THE BK mod. It's easy on yr carb and you will like the results. In fact I suspect the BK did more for my low end than the needle. It's fun to be able to wack the throttle any time you want and get instant response!


  • R_Little

Posted December 14, 2002 - 07:45 AM


Sorry guys the other needle I'm considering is an EKP not an EKN.


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  • tctrailrider

Posted December 14, 2002 - 08:13 AM


RL, EKP vs EJN. The K is 1/2 clip leaner than the J. The P is one letter leaner on the straight diameter than the N. The higher the letter the leaner it gets. O is not used. With the EKP. E is the taper, K is clip position, P is the straight diameter.

  • tctrailrider

Posted December 14, 2002 - 08:23 AM


EKP vs EJN, With the EKP the E is the taper, K is the clip position, P is the straight diameter. As the letter gets higher the needle gets leaner. O is not used. The K is 1/2 clip leaner than the J. The P is one step leaner than the N. (O is not used) Good luck.

  • R_Little

Posted December 14, 2002 - 10:21 AM


Thanks TC. The EKP is leaner in 2 dimensions. I thought so.

I've got a 162 in my box. I'll put that in first, see what happens. I don't know if it will be enought. If not, I'll put the EKP in.

If I need to go to a 160 main I'll have to order it.


  • jmiakaike

Posted December 14, 2002 - 11:00 AM


your stock main is 165? mine was 162? (on 2 426's i have seen, stock was 162) see... that black art thing again, i am at about sea level.. maybe 100ft tops... but sounds like you had fun anyway!!! i am jealous.. engine still apart on table :)

  • R_Little

Posted December 14, 2002 - 02:14 PM


My stock main was a 165. I don't have a 426 though. Mine's a 2000 wr400.

Stock Needle was a DRS, does the 426 have a different needle?

It is kind of fun getting intimate with the bike. I like to know what is going on with the stuff I ride and drive. It's really too cold and wet to ride now anyway.

What I don't know is whether I'll get any more power out of that YZ pipe though. At least it's much lighter though.

  • dominator426

Posted December 14, 2002 - 11:39 PM


R Little,
E needles usually run with a MFJ of about 7 numbers smaller than with a D needle to maintain desired and optimum ratio at 3/4 to full throttle. This is due to E's bigger taper,(1.0 degree from 0.75 degree) drawing more fuel from MFJ at high throttle opening.

  • R_Little

Posted December 17, 2002 - 10:04 AM


Thanks Dom:

The 162 MJ seemed to clean up the top end a little but brought back the popping on decel and seemed to weaken the mid a little. Overall not a positive experience in my book.

I think it's time to try Taffy's air jets. Does anyone know where I can find them in the states?

If that don't work, it's off with the yz can and back on with the stock pipe and jetting.


  • tctrailrider

Posted December 17, 2002 - 05:39 PM


Your running good at the top ( main jet) and popping and seeming lean in the middle (needle). How about raising the needle a clip leaving in the 162. With Taffy jetting, he uses very lean jets with a very rich clip setting 4-5th clip. stocks a lot of jets.

  • Steve_WR400F_#61t

Posted December 17, 2002 - 08:07 PM


I'm planning on doing the BK soon. Just don't know when I'll get to ride again. The first storm of the year has hit and now we've got a few inches of snow around the house. More forecasted for this coming weekend too.

Does the BK do anything to your jetting? Leaner or richer on the pilots? Since I'm trying to adjust jetting now anyway, how does the BK mod effect jetting? Should I be dropping to a 42 pj from the 45? I've also got the EKN needle on order, will the clip position need to be something other than the suggested #3 spot? Right now I'm leaning towards Yamakazi's suggested settings.

Now if the needle would just get here, the weather clear up, and time open up for some testing...

  • Taffy

Posted December 17, 2002 - 10:38 PM



you're starting to sound like an old record! so calm down mate!

now there is a lot of tosh talked of the BK or Taff mod; all you have to do is cut it down and for most people it leans off the fuel in an area that was overly rich anyway.

most people agree that the #45 PJ is overly large and if you look at talljohns set-up he has come right down. all you've got to do is fit the bloody stuff and try it.

if it doesn't work first time; so what!

the idea of you being snowed in all winter "with the needle and SJ on order" doesn't bare thinking about.

i think i may have to make a personal delivery myself just to get a rest...

i hope you get sorted soon. just fit it!!!!

get on with it and as i always used to say "does my bum look big in this!"



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