jetting information overload !



8 replies to this topic
  • XC800.X

Posted July 21, 2002 - 09:28 PM

#1

Sorry for asking another jetting question.I've done lots of searches and I just can't get a handle on it.
I have a 01 WR 426 Candian with a YZ muffler,no lid.
165 main
42 pilot
DQR #4
3 turns out PS
I have some sputtering under light throttle at mid and up RPM's.I get rid of most of the sputtering if I move to #2 but the popping on deceration increases.Also this seams alot leaner than stock when shouldn't I need more fuel?This setting is pretty much stock except for the fuel screw and it's seems the best compromise without changing parts(tried the 170 MJ with different needle positions and fuel screw adjustments)
It's not horrible the way it is.It runs a hell of a lot better than stock.I'm still running the factory plug and it doesn't stall if I wick the throttle too fast.Should I go to a different PJ and try different needles ?It seems I need to be leaner to get rid of the light throttle sputter but richer to get rid of the popping.I'm just confused so any help would be appretiated.
P.S.I live faily close to sea level and I can't find any leaks in the exhaust or intake.
Shawn :)

  • blue_beast_wins

Posted July 21, 2002 - 02:55 PM

#2

The light throttle splutter will be your needle position, drop the needle to clip position #3 with a 160 mj, Then readjust the screw, that should fix the popping, These bikes are way too rich from factory.

  • YamaMoto

Posted July 22, 2002 - 07:22 AM

#3

I have an 02 Canadian, mine did the same thing. Its running out of gas at low throttle openings. If you give the throttle a little twist it clears up because of the accel pump sqiurt. At that point you are on the straight part of the needle. The R in the needle part number is the straight part. Dropping or raising the needle did not help in 1/8 to 1/4 steady throttle. I am sure a richer needle will help. Mine cleared up with a EMN neddle. Still working on making it PURRRfect.
Matt

  • dominator426

Posted July 22, 2002 - 06:51 PM

#4

I am also near sea level with my Canadian 2002 WR426 and, after doing BK mod, removing airbox lid AND screen, I had to switch to a one step richer DQQ needle (pos#3) and #172 MFJ. After sealing air cut valve (on 2002), I had to switch to #38 PFJ open 1 turn and I'm waiting on a #85 PAJ (stock is #75) to lean out pilot a bit more...
So it sounds like you're lean on needle and trying to compensate with pilot. What size pilot air jet did you have? You may also be successful with "EMN" type needle which requires smaller MFJ but I'm not sure how the straight portion would compare to a "DQQ"...

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  • James_Dean

Posted July 22, 2002 - 09:06 PM

#5

I aggree with everyone on this. If your manual shows a DQP needle option, that would be worth trying in clip #2-3. It's a step beyond DQQ.

This is close to a DVP#4-5 which helps with the lean 0-1/8 and the needle clip can stay at 2-3 to help the slightly higher range sputter richness. (Second letter just shifts the clip position)

Last letter N is only slightly richer 0-1/4 throttle than the last letter P, then Q, then R is gets to be too lean.

When we start talking about Exx needles, this changes the taper of the needle to make it steeper than Dxx. The pointed end becomes smaller. It adds fuel (richens) at mid-upper throttle and can add too much on top unless the main jet is downsized.

James

  • XC800.X

Posted July 23, 2002 - 04:41 PM

#6

Thank you!
THe DQP is shown as an option so I will try that soon.I think I'm sort of getting a handle on it maybe,kind of.I'll guess I'll keep studying these posts. :)
Shawn

[ July 23, 2002: Message edited by: XC800.X ]

  • James_Dean

Posted July 23, 2002 - 06:30 PM

#7

Take a look at these graphs to see some of the specific effects of needle diameter, clip position, and taper versus throttle position:

http://www.thumperta...raphs.htm?id=15

  • dominator426

Posted July 23, 2002 - 10:25 PM

#8

With all due respects to James Dean, I feel you may be overdoing it with the 2 step richer DQP needle and end up more confused. The DQQ needle is substantially richer than stock and, in my case, had to be leaned to position #3...

[ July 24, 2002: Message edited by: dominator426 ]

  • James_Dean

Posted July 24, 2002 - 08:20 PM

#9

dominator426,

You could be right, the adjustment to DQP was meant to be significant. The last letters commonly used with Dxx needles are- M, N, P, Q, R, S. As you can see xxP and xxQ are in the middle. Considering the fuel screw is out at 3 turns, this may help reduce that and the popping on deceleration.

The first WR400's and most KTM's use DTM. The first YZ400's and the leaner KTM "-G" California models use DVR. The D-P will fall in the middle.

What I also see here is most bikes with a DQ- needle need a leaner clip position #2 or #3.
DQ-#3 = DT-#4.5 = DV-#5.5

Jetting is trial and error with a little experience and common sense thrown in. We'll have to see where Shawn ends up at. :)

James




 
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