Please help yz426

6 replies to this topic
  • Griggs813

Posted March 26, 2014 - 11:45 AM


I just got a 2001 yz426 will only idle with choke on I live in up state ny so I know it's been cold the bike has a header and pipe and a r and d fuel bowl no air box lid bike runs so good with the choke on when I turn it off it back fires and just don't run good i don't know if carb is dirty just been waiting for warmer weather what do guys think I should do

  • grayracer513

Posted March 26, 2014 - 12:10 PM


The pilot jet, or a part of that circuit is either clogged, partly clogged, or the jet's too small for the cold weather.  What part of the country are we talking about?

  • cowboyona426

Posted March 26, 2014 - 12:15 PM


Did you have the carb slide out recently?

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • Griggs813

Posted March 26, 2014 - 12:44 PM


Orange county New York and I've done nothing to the carb at all I just got the bike and rode it once for about a half hour

  • SC_Spode

Posted March 26, 2014 - 01:21 PM


Listen to Gray on this one - it's the most common issue for carbureted bikes when they have been sitting for a while. 


More than likely it's lean for one of two reasons: restricted fuel flow in the pilot circuit from fuel varnishing (or dirt) or the pilot jet is undersized.


Varnishing is a common cause if it's been sitting for a while.


You may want to determine where the fuel screw is presently set and then back it out in 1/4 turn increments to see if that helps. If it does, then you know the circuit isn't completely plugged up. I wouldn't go more than 4 turns out with the screw for fear of losing the spring tension on it and having it fall out. (I'm sure there are plenty of threads on here explaining how to adjust the fuel screw and its effective range so I won't go into detail here.)


The pilot jet has the smallest orifice so it's the first one to clog due to varnishing from old fuel. It manifests itself the way you described or it won't idle at all. The choke provides supplemental fuel while it is activated that allows the engine to run. Once the choke is cut off there is either insufficient or no fuel passing through the pilot circuit to fuel the engine. 


The varnishing/souring of the fuel happens much more quickly with ethanol "enhanced" gas. We have access to ethanol-free around here so I avoid it in virtually everything I own, especially small, carbureted engines.


Here's a link to a site that you can use to find stations that sell ethanol-free gas in your area:


If cleaning doesn't cure it then try a larger pilot jet in one-step increments.




Hope it helps!



  • grayracer513

Posted March 26, 2014 - 01:27 PM


It merits inspection, but you might also read up on the adjustment procedure and try that just before pulling the thing apart.  The cold really does have an effect.  What the cowboy is referencing is the fact that the carburetor slide has a vacuum release plate on the engine side that's easily installed upside down by mistake.  It has a round end and a "square" end that has a hole near the edge.  The square end goes down.


Cautions about the carb:


1) Don't remove the throttle position sensor, the black device on th eleft side with the wires coming out.  It's no fun to re-adjust.  Don't submerge it in carb dip, sheep dip, bean dip, or anything else to soak, either. 


2) Don't remove the four screws you will see inside the carb at the top of the float chamber that hold the upper and lower halves of the carb body together, either unless it's absolutely necessary AND you already have the replacement gasket in hand.  To my knowledge, Zip-Ty Racing is the sole source of these, and they are usually unusable once you disassemble the carb.


Then, read this: http://www.thumperta...o/#entry6879695


These two may help as well:



  • Griggs813

Posted March 26, 2014 - 04:02 PM


Thanks guys a lot I'm new to this fourm and didt think I would hear back so soon I'm gonna try a few things this weekend today's temp was like 34 Sunday gonna be 60 I hope I will keep u posted thanks again

Related Content


Megabomb Fitment by 288yz450

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • 1 reply

Snake pit oct 30th by The Anvil

Dirt Bike   Dirt Bike Regional Discussion   California
  • Hot  293 replies

Chubby dad, looking at bikes , First trip to the orange/black forum ! by Slow_ride

Dirt Bike   Make / Model Specific   KTM   250-530 EXC/MXC/SXC/XC-W/XCR-W (4-Strokes)
  • Hot  28 replies

The "going back to the other darkside" adventure... by Monk

Dirt Bike   Make / Model Specific   KTM   250/350/450/505 SX-F & XC-F (4-Strokes)
  • Hot  113 replies

Yamaha YZ450F 2017 by Chris.GVS

Yamaha YZ450F 2017
  • * * * * *
  • 1 review
  • Last review by Tommyk_55
  • On January 15, 2017

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.