yz426 wont start!

11 replies to this topic
  • superjetrider18

Posted March 04, 2013 - 05:29 PM


I got a 2001 yz426f that i traded for my sled. When I got it, I could barely get it to start, only with the throttle wide open. There was coolant in my oil, soo I tore apart the motor, put all new gaskets in it, and put it all back together. Now thats its all back together, the bike still wont start. The bike spudders, but wont stay running. Im pretty sure its not my timming because it seems to be adjusted correctly (following all the online directions). Any other ideas what it could be? I just wanna get out there and ride. lol

  • capt justin

Posted March 04, 2013 - 05:36 PM


valves probably need adjusting, pilot jet clogged, old gas, could be any of these.

  • superjetrider18

Posted March 05, 2013 - 06:14 PM


Okay, im new to 4 strokes, always just have ridden 2.. I took my head and jugg off to pit a new base gasket on, would that of messed up my valve? I didnt mess with them, but just wondering if they still should be good if I didnt mess with them

  • superjetrider18

Posted March 05, 2013 - 07:02 PM


Valves* hard to type on this phone lo, but the bike also wont run a starting fluid, it still just spudders

  • Pooley

Posted March 05, 2013 - 08:38 PM


...When I got it, I could barely get it to start, only with the throttle wide open...

Never, ever do this with your YZ again. People here will be able to post pictures of kick-back injuries. Twist the throttle 1 or 2 times to prime things, and then follow the starting ritual with your hand AWAY from the throttle tube, a lot of folks grab the front brake reservior.

Remember: 1 or 2 twists to prime (if necessary) when cold, slowly bring the piston to top dead center, pull the decomp and move the kickstarter to move the piston just barely past TDC. Let go of the decomp and kick like hell.

Check the carb jets for blockages and then post your elevation, temperature, mods and jet sizes. On a bike that has been sitting any length of time, the jets are plugged/varnished 75% of the time even if they are appropriate sizes.

  • superjetrider18

Posted March 06, 2013 - 10:58 AM


Well right now, I dont kno the sizes of the jets, but I live in michigan, so around 35 right now, and I got a white brothers exhaust, bike sat outside all summer, had water and antifreeze in my oil, still just spudders if I try pole starting it

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  • Pooley

Posted March 06, 2013 - 01:32 PM


Well, for Michigan with the WB exhaust you will need either a 45 or 48 pilot jet, 170ish main, needle in the 3rd or 4th position. The air jets you can pretty much leave stock.

No matter what, I would take the jets out and meticulously clean them and then use compressed air to blow them out. While the carb is out, clean that as well. Maybe even change the sparkplug. The cleaner everything is, the easier it will be to diagnose the problem. Anything fouled will just make it almost impossible to troubleshoot.

Because it is so cold out, you will probably need to richen up the fuel screw on the bottom of the carb, or it will pop like crazy if it was still set at a "summer setting". Turning the fuel screw out opens it up and allows more fuel, richening the mixture. If you have to open it up any more than 2.5 turns out from closed, you are definitely way to lean on the pilot jet. There are many stickied posts on how to tune the pilot jet, which is usually the first thing to sort out.

Once you've got everything clean/new and determined the jet sizes it'll be a lot easier to get things squared away.

  • superjetrider18

Posted March 22, 2013 - 03:06 AM


Got the bike timed and the valves done correctly now and bike starts right up, but now the bike is mixen the coolant with oil, any ideas what the problem could be?

  • etuke

Posted March 23, 2013 - 08:53 AM


water pump shaft and seal.

  • grayracer513

Posted March 23, 2013 - 09:42 AM


water pump shaft and seal.

The water pump can't mix oil and coolant. There's an escape port under the pump that allows either fluid to run to the outside without threatening the other volume.

More probable suspects would be the head gasket and the seals at the water passages from the right side cover and base gasket.

  • superjetrider18

Posted March 24, 2013 - 05:42 PM


Okay im thinkin it was the head gasket,, being after runnin for like 2 mins, it started leakin oily colant outta the gasket, and then wouldnt start again.. now you can barely kick the bike over without the decompression, its alot harder then before it started leaking. could that be also from the headgasket?

  • superjetrider18

Posted March 27, 2013 - 10:10 AM


Could it be from the gasket, or no?

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