Patchy mid range power due to jetting?

49 replies to this topic
  • Redbird87

Posted May 09, 2001 - 06:29 PM



As a follow up to previous post a few weeks ago on this thread:

I have stock jetting on a 2001 WR426. Turned fuel screw out 1/8 turn. This alone improved "cruising stutter" condition significantly. It is so much better that I am not willing to jack with it more for fear of screwing up a good thing.

  • scoobydoo

Posted May 31, 2001 - 11:48 AM


did you fix the bikes jetting, my 01 426 is terrible on the sanme throttle openings as yours, btw did you enjoy Fast Eddy?


  • Derek_Burns

Posted May 31, 2001 - 02:07 PM


Hi Scooby,
The Fast Eddy was brilliant, I was gutted to see the chequered flag. I was slow to start, but as the race progressed, I got the hang of it. Me and 2 mates might be entering the Trentham Gardens on the 24th, (if its not too late for an entry)BTW... I think I need some tips on cornering in deep sand :).
the patchyness on my bike is much improved after lowering the needle a tad, especially now the warmer weather is in, but I still need to tinker with it to erradicate the problem completely, though I've been too busy recently to get a chance to focus some attention on it. Taffy and james dean have given some good guidance, of which I've still to follow completely.
It was good to meet you on saturday....
maybe we will meet on another raceday.


  • WR400inOZ

Posted May 31, 2001 - 06:21 PM


Taffy is the Yoda of this forum.

  • scoobydoo

Posted June 04, 2001 - 09:02 PM


finally got my bike to run ok, have removed the airbox lid, but had to drop the needle two clips!! Had to adjust the pilot screw as it was then too lean down low but it now seems to be ok. If you are at a loose end this sunday (10/6/01) come down to blandford in dorset and have a look at one of our events(southern counties enduro club). It's a full entry I'm afraid but it will be good spectating, you'll find all the details on

cheers m8

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  • James_Dean

Posted June 04, 2001 - 12:21 PM



Is that needle a DRQ #2 clip ?
Or was it DQR, as Derek posted earlier?

Either way, it is good to hear some progress on this.


  • scoobydoo

Posted June 06, 2001 - 12:27 AM


thats a standard euro needle, I believe it's a dqr

  • Derek_Burns

Posted June 07, 2001 - 11:19 AM


Looks like Taffy's diagnosis worked for you.

I still haven't focused my attention on perfecting the jetting, I've had so much going on recently and the bike is performing better these days, although theres still a trace of the old bug. maybe the warmer weather has something to do with it.
Thanks again to all who have contributed to the diagnosis of this problem, I don't want to seem like I'm ignoring all the good advice.
Scooby, what pipe do you have on your bike?,
and did you go to YZ timing in the end?
I would be intrested to hear the outcome, as your bike seems the same spec as mine.


  • tonymontana

Posted June 07, 2001 - 04:13 PM


Originally posted by Mojo:
Just heard today about a wire, if clipped eliminates the chugging I'm hearing described in this post. I'm learning the electrical system on this thing. The yamaha service guy was speaking with the regional service tech and apparently got this information. It has something to do with the emissions requirement and causes the 4th and 5th gear stutter described by many of you. I believe he said it was the gray wire coming out of the CDI. When I get a better description I'll share more.


For what it is worth, I was told that the ignition retards in the mid range for noise emission tests. I am from Australia, and will chech if mine has a grey wire. Maybe that is what the grey wire does.

Tony Montana

  • scoobydoo

Posted June 21, 2001 - 02:11 AM


My bike now has an fmf powercore 4 Q pipe, otherwise it is standard. I haven't yet tried the yz timing mod. A mate of mine from the Isle Of Man was over for the fast eddy at matchams. He, in turn is good mates with David Knight and rides out with him regularly, any how the word from "knighter" is that the cam timing is actually only half a tooth away from yz timing. This comes from the belgarda yamaha world enduro championship team, who also run 4 stroke wr's so I guess could well be true. after hearing this I decided not to bother, it's not as though I'm looking for power anyhow. I have to say that the power delivery/amount on the 426 is night and day compared to my '00 400. It seems much stronger and controllable down low so I have decided to leave it for now.

hear from you soon m8



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