2001 YZ426F Won't Start

Yamaha YZ426F 2001

11 replies to this topic
  • buck424moto

Posted March 24, 2014 - 05:56 PM


I have a 2001 YZ426 that will not start. It is a friend of mines and we have been working on it for about a week. We have completely cleaned the carburetor, check and shimmed the valves, checked timing and reset it. It has fresh gas, good spark with a brand new spark plug, It is getting fuel all the way through the system, we can't see anything visually wrong any electrical parts. We have tried kicking and kicking, bump starting, pulling it. We have tried using a little starting fluid. We haven't got any kind double roll on the motor or any sign that the motor is trying to start at all. We don't know the last time it ran, He bought it from a guy who never got it start although didn't know what he was doing, and the same with the person before him. If you have any advice it would be very helpful. Were hoping to not have to tear down completely. 

  • G-BRO

Posted March 25, 2014 - 12:50 PM


You said that you "checked and reset the timing?". What was the timing set at before and how exactly do you have it set now? 

  • buck424moto

Posted March 25, 2014 - 02:20 PM


As said originally whoever had it before didnt know what they were doing. It was two teeth off on timing. We reset it to what we believe is factory being the dots lining up with E and I on the cams flat with the top of the head and I lined up in the marker on the side case. 

  • Yammer-Hammer

Posted March 25, 2014 - 05:12 PM


How does the compression feel? Does it have the auto decomp cam?

  • buck424moto

Posted March 25, 2014 - 06:43 PM


Compression feels like a 426 should. I put all 180 of myself on the compression stroke it stood still for me. It does not have the auto decompression. It still has the lever. 

  • Yammer-Hammer

Posted March 25, 2014 - 09:24 PM


The only other problem it could be is the jetting. I would check and make sure the fuel screw in the bottom of the carb is still there, and also make sure that the oring, and washer for the fuel screw is still all there and that the o ring is intact. I would the check and find out what size pilot jet is in it and compare it with others. Also make sure that you dong twist the throttle at all when your starting it. These bikes are very sensitive to the pilot circuit being perfect and if its off just a little bit then the bike wont start or wont idle/run right.

I would definitely mess around with the pilot circuit which also includes the height of the slide. Which is 3.4mm or (.134in). Stock

Edited by Yammer-Hammer, March 25, 2014 - 09:32 PM.

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  • Yammer-Hammer

Posted March 25, 2014 - 09:36 PM


Heres the jetting for my '02 at 0-2000ft in 30 to 70 degrees f weather.

Pilot - 45
Main - 165
Needle - OBEKQ in 4th clip
Fuel screw - 1 and 3/4 turns out
Pipe - all stock w/spark arrestor

I also have the BK mod with a 1 sec squirt duration. But that has nothing to do with starting the bike only has to do with throttle response

  • buck424moto

Posted March 29, 2014 - 06:29 PM


We got the bike to start and run. We currently have a Pro Circuit 304 full exhaust on it. It came with that and a 185 main jet. It will idle fine with the choke on. As soon as we turn the choke off it acts like its starving for fuel. I think the 185 is way to big. I fell like a 170 should be good enough. the only way to get it to idle close to ok without the choke is with a 165 Main with the fuel screw 4 turns out. Any suggestions on a reference I can use or look at to help figure out a good jetting? The needle is also on 4th clip, and With 4 turns out and 165 it dies as soon as we touch the throttle. 

  • rogo1

Posted April 08, 2014 - 05:12 AM


pilot jet controls idle circuit what size pilot are you running? is it a new pilot? it doesn't take much to plug the pilot up, this happened to my bike cleaned the carb and replaced jets with new ones. problem solved. but my bike was acting the same as you describe would only run with the choke on due to a lean pilot - partially pluggedup pilot jet.

  • grayracer513

Posted April 08, 2014 - 07:06 AM


The 185 is way too big, but that's not your idle problem.


If you look in the forum index, there's a pinned jetting database.


As to your pilot, which is obviously either too small or clogged, read: http://www.thumperta...ircuit-setting/


...and : http://www.thumperta...o/#entry6879695

  • motohead 023

Posted April 09, 2014 - 05:03 PM


spark plug

  • Deere13

Posted April 15, 2014 - 08:12 AM


I have a 2002 YZ426 with a Powerbomb and a Powercore 4. The air box lid was removed. I'm running a #170 main and a #45. I forgot what slot my clip is in on the needle. It is whatever JD Jetting recommended for the elevation I ride. It runs great.

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