WR426 doesn't idle after throttle roll off

7 replies to this topic
  • ioan_vapi

Posted January 03, 2009 - 02:34 PM



I'm the new owner of a used WR426. It's my first offroad bike. It looks like I get used with this bike and I observed the detail described below.
When I ride the bike in the first gear and I roll off (release) the throttle the engine doesn't idle but stays little higher even I roll off the throttle by hand. More than that, if I want to idle the engine I have to use the rear break.

Another scenario: I pull the clutch, roll off the throttle and the engine doesn't idle but it's a little bit higher. At this moment, if I release the clutch lever then the engine idle when the first gear is connected. Very important here, when I pull the clutch again, the engine idle.

First assumption is about throttle cable but I do roll off the throttle by hand, not just release it. In neutral I roll on the throttle 1/4 and release it immediately. Very rarely the engine idle after this action.

The second assumption is about the carburetor. Maybe a cleaning is required but the engine (+the carburetor) should be consistent and doesn't idle in above scenarios.

The third assumption is about TPS. I read on this forum about TPS mod and I disconnected it today for a while. It looked like the idle is better. I'll continue to experiment with TPS on/off. I cannot figure out how TPS can influence idle.

Please, can someone give me some suggestions or logical explanations?


  • 43Duc748

Posted January 11, 2009 - 05:15 PM


Sounds like clogged jets. I had the same problem on my bike and the advice was that it was a hanging idle brought on my clogged jets. I took my jets out the other day and cleaned them. I haven't yet taken it out to ride, so I don't know if it fixed the problem. I have high hopes!

  • bluebreadtruck

Posted January 11, 2009 - 07:25 PM


yeah typical clogged idle jet,.,..clean the carb

  • William1

Posted January 12, 2009 - 03:21 AM


Yup, partially clogged pilot jet. If a replacement is available, simply replace it as cleaning it 100% can be hard to do.

TPS affects idle because it changes ignition timing. Check to make sure it is adjusted correctly.

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  • Dee Perry

Posted January 12, 2009 - 08:58 PM


X2 clogged jet. For 5 dollars dont even try to clean it. Replace it.

  • TRUE_2_YAMAHA_001

Posted January 12, 2009 - 10:19 PM


The carb is dirty and your float could be sticking.

  • Scotty426

Posted January 13, 2009 - 12:00 AM


I went through living misery on my YZ 426. I was running too lean on the pilot and it would run away at idle or die in alternating sequence, no rime or reason. I cleaned everythig and adjusted the float all to no avail. I needed more pilot and more fuel screw. ANd no, it didn't lean pop like you would expect. Don't know why, maybe my quiet muffler. Good luck. The 426 is a keeper when you get it right.

  • ioan_vapi

Posted January 17, 2009 - 01:45 PM


Thank you all for your suggestions.

Last time I tried the mod for airbox and I observed an improvement but still sometimes the idle is higher. The next step is to clean the carb and all jets. I'll check the TPS voltage too.

I never opened the carburetor and I don't know what jets I have. I'm thinking to buy a JD Jets Kit.


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