I am no mechanical doctor please confirm my diagnosis

8 replies to this topic
  • finglan

Posted October 27, 2001 - 01:39 PM


The last two short rides on my 01 WR 426 I got alot of sputter at about half throttle in any gear. Much more pronounced than when the grey wire was connected. If I gave it more gas it would go away. I changed the plug at about 100 miles and it was a little brown. The bike has about 600 miles on it now and the plug was full of carbon along w/some carbon in the head pipe.
The air box lid is removed and I have a YZ throttle stop in. I have a Baja Designs exhaust baffle. It has always started on the second kick and if I dumped it w/the hot start it would start on the first kick. So I have never made any jetting changes.
I cleaned the carb and raised the needle two clips. My thought was that it has been running a little rich and the plug was starting to foul. It is in the basement for the winter so I will not be testing the jetting change until spring time. I have rode it when it was colder out then now and it ran fine. I am wondering if I am heading in the right direction for the fix.

  • Taffy

Posted October 27, 2001 - 03:12 PM


i was reading your diagnosis ands i thought to m#yself mmmmmm, down a clip, nope! down two! and then i read that you've gone up two clips.

put it back as was.


  • DOC

Posted October 27, 2001 - 06:09 PM


He said he raised the needle two clips, so he must have lowered the clip two spots.
Take it back to clip no.3 and if still no go, try no.2. Everyone seems to be running too rich.

  • MN_Kevin

Posted October 28, 2001 - 12:22 AM


Since it is put away for the winter, pull the carb, completely disassemble it, and clean it THOROUGHLY. The weak link on the 98/99's is the accelerator pump system...very prone to dirt intrusion.

I know the 2000/2001's use a completely different setup for the AP.

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  • finglan

Posted October 28, 2001 - 04:12 AM


Yes, I raised the clip two positions droping the needle thus leaning it out. According to the manual. I have read most of the previous posts on jetting. Being new to this I just get information overload. I just want to take it one step at a time and get someone elses opinion.

It sounds like the bike was running a little rich due the the plug and pipe?

Start with leaning out the needle jet one clip not two?

I did clean the carb thoroughly. It did have a very thin layer of black film on it. I could see this by rubbing my finger on the slide or throat and there would a small amount of this residue on my finger.

Thanks guys.

  • Taffy

Posted October 28, 2001 - 01:11 PM


i'm confused.

if i understand you correctly finglan, what you're saying is that you put the needle up two clips (so you moved the clip down the body of the needle?) this made it ridher and the bike ran worse?

you then say that you raised the clip two places and this leaned it?

look, from your original diagnosis you should drop the needle down one clip from whatever you started with, OK.

we'll help if we can.


[ October 28, 2001: Message edited by: Taffy ]

  • finglan

Posted October 29, 2001 - 05:17 AM



I looked in the manual and read, to lean the bike out to raise the clip. So I raised the clip up two posistions ( not the needle ). The clip is now further away from the pointy end of the needle. I assume this would allow the needle to seat further down allowing for less gas to flow.

I guess what I am trying to confirm is the following:

If the bike was running a little rich it would begin to foul the plug over time and I would have the symtoms I described. A bad sputter at a constant throttle postion. Alot of carbon on the plug and pipe.

If I should start at the needle jet to correct this.

  • Taffy

Posted October 29, 2001 - 10:31 PM


well you've certainly gone in the correct direction with the needle.

if you don't mind i'm sure we'd like to know you're full jetting details if you can find them.

some of the 426 runners are on clip 2 and counting also they're using the 42 pilot jet so you might feel inclined to join them.

one things for sure, if the only cure is to whack the throttle you're rich.

another thing to remember is that the needle richness is controlled as much by the MJ as the needle clip position with this carb.

so review you're MJ size. to find out if you're getting the clip right on the needle accelerate to flat out on a smooth road and then close the throttle for two seconds then gas it up again. you'll soon know whether it's right.

good luck


  • finglan

Posted October 30, 2001 - 03:38 AM



Thanks, I do think the clip is now on posistion #2. The rest of the settings are stock.


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