01 426 YZ coughs a little on idle/midrange

5 replies to this topic
  • quartzite

Posted December 02, 2004 - 06:49 PM


My 426 YZ coughs a little on idle/midrange. I thought I'd ask you guys if you thinks it's valve lash or some other issue. Thanks!

  • YZ250F_Rider

Posted December 02, 2004 - 06:52 PM


lift the needle a notch. It's cold out.

  • mikev7

Posted December 02, 2004 - 08:41 PM


I just rejetted mine cause it was coughing, it's the weather. I went up on the "jet needle" one notch and turned the pilot "fuel screw out about 3/4 of a turn to richen out the low end. It stopped. It's easy, just pop the sub frame off, then the carb. Clean it and take the needle under the allan wrench shaped screw and put the cir-clip one groove down. Put it back then turn the fuel screw on the bottom of the carb 3/4 of a turn. I'm at sea level elevation.

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  • sirthumpalot

Posted December 03, 2004 - 03:34 AM


By midrange I assume you mean small throttle openings (idle - 1/2)? First clean the carb, you will be surprised what a slightly dirty carb will do to these things. Adjusting the fuel screw will make the most difference in the idle to 1/4 throttle range. If this is where your stumble is then play with the fuel screw and possibly the pilot jet if the screw alone doesn't give you enough adjustment. From about 1/4 - 3/4 throttle, the needle is going to make a significant difference. There is some overlap, but you get the idea. Raise the needle (lower the clip) to make it richer. If you don't already have one, I very strongly recommend something such as the Zip-Ty Fuel Screw. With one of these you can adjust the fuel scew with your gloves on, no more searching for that tiny screw! :cry:

If your valves were tight enough to hang open and cause a stumble, then it's very likely that you would experience difficult starting and unstable or no idle as well.

  • skthom2320

Posted December 03, 2004 - 08:57 AM


Forget cleaning the carb. You can change the needle clip position in about 15 minutes without even taking the carb off the bike.

I just take it loose from the airbox and intake boot and let it hang from the throttle cables. Then remove the plate off the top of the carb and the allen that holds the needle in. Remove the needle with some needle nose pliers, put it in a plastic baggie so the clip doesn't go flying when yotake it off, change the position, and put it all back together.

If it still does it then you can go spend the time to clean the carb. But that takes a hell of a lot more effort than what I suggested. :cry:

  • quartzite

Posted December 03, 2004 - 12:37 PM


Thanks fellas. I think you guys are right about temp/jetting~the low has been -17 and the high 25 here...I'll tinker this weekend.

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