Bike will not start or run right.

I have a 01 YZ426 and i just pulled it out of the garage the other day. it was about 40 degrees outside. for one thing, the bike will never start inside a warm garage unless you kick it over about 20 times. Today when i got it out i pulled the choke out, and i didn't touch the fired up after 10 kicks or so and sat and spit and sputtered until it just wouldn't run anymore and it died and it would not start again. I pulled the plug out and it was black and sutty. I've read on how the CDI's have been going bad on them. could this be my problem or am i doing something wrong cause i am really getting fed up with the bike the way it is running. it will be fun once i get it going but until then someone please help.

thanks so much.


Pete- if you haven't yet, try changing the plug. I've spent alot of time working on bikes with some kind of problem and ended up solving the whole problem by changing the plug. If this doesn't do it post back and some of the guru's around here should be able to fix you up...


I purchased a 01' 426 that would act the same way. After three rides on the same plug it would sputter and not run well. I would change the plug and it was like a new bike. Went to the dealer where I got it and He replaced the CDI with a new bike he was assembling, no change. Then he replaced the mapping circut in the carb. This solved the plug problem, but the bike didnt feel as good as it did with a new plug, so he is replacing the carb to fix the soot on the plug. Hope your dealer is as good as mine!

Start with a fresh plug - then be very careful not to apply quick bursts of throttle until the bike is fully warmed up (let idle for at least 2 minutes, then only apply throttle slowly). When you blip the throttle you shoot straight gas into the engine, which when the engine is cold is more than the plug can handle. The natural reaction when a bike starts to miss is to blip the throttle to warm it up, but this actually makes it worse with these pumper carbs! I have not fouled a plug in 2 years on my 98 WR400 since I started paying careful attention to that. Have a stack of about 10 plugs before I figured it out. I also switched to a CR7E plug (hotter) but not sure about that for a 426?



98 WR400F, YZ'd cam, YZ muffler

I just fouled my thrid plug this same way. I rode it a couple of times, then I started it in my garage and it ran for a 30 seconds then died plug fouled.

The bliping the throttle makes sence. If it is not warm it will be getting a alot of fuel while cold.

I have a hard time believing the CDI is bad. It could have bad mapping, but then all the 01 should have the same problem.

I do like the idea of the CR7E plug. I am going to try and find some.



01 YZ426F #85 Vet C

One more thing - I see you mentioned 40 degree weather - when it is that cold I usually cover one radiator with a piece of cardboard. There is no thermostat so the whole engine (and the plug) run too cold in cold weather (in my opinion). I have not had any overheating trouble, but only do this when the temps are around 50 or lower. One more thing to try .... Hope you have some luck I know I am waaay hapier with my bike after fixing the fouling thing. Very frustrating at first - I am very good at removing the seat/tank though!



98 WR400F, YZ'd cam, YZ muffler

Pete: I hope you aren't leaving the choke on for an extended period. About 20 seconds should be the maximum...and less as the ambient temperature rises. I doubt that I've ever left my choke on for more than 10 seconds...even when it was in the low 30's out.

[This message has been edited by Boit (edited 03-15-2001).]

Good comments by everyone.

Be sure to use a slightly faster idle too. This will allow turning off the choke early ( less than 20 seconds) and helps avoid the need to twist the throttle to keep it running.

How many turns out is the pilot screw?


I think I may have killed the last plug leaving the choke on too long. Since, I fouled the second plug, I have been letting it run longer with the choke on to get it too warm up and not die.

I will turn the idle up a tad and use less choke.




01 YZ426F #85 Vet C

[This message has been edited by forloop (edited 03-15-2001).]


best thing to do is leave the bike with me for a few months and I will sort things out for you. I may even be able to diagnose a bad midvalve in the forks........

Thanks for the help everybody. I picked up some plugs today and i will see tomorrow if i can't keep the thing running. I really hope i do not have to get the carb replaced like a lot of people are talking. When you guys first start the bike up do you usually pull the choke out and that's it or do you give the throttle a few turns? just curious on that. Thanks again.


P.S. DhLaw- i'll keep that in mind :)


This routine has worked for me since I have had my 98 YZ400. It works on my 01 too.

1. turn gas on

2. pull choke out all the way

3. using comp. rel., kick through 3-5 times

4. kick to start

5. leave choke on for no more than 10-15 secs

6. shut off choke and let warm up (may need

to turn idle up a bit)

7. go ride!!

This starting routine was given to me by a pro who has raced 4-strokes for many years. I have used this technique since I got my 98 YZ400 at the end of 97. I have never had a problem starting the bike this way (either one).


Something just occured to me that was told to me by my riding buddy. He said he has noticed that if he closes the petcock at the end of a ride and let the engine run about 20 seconds or so before shutting it off, that his bike starts much easier the next time. I have ALWAYS done this with my 426 and my bike starts easily no matter what the temperature is outside. I only do this to prevent fuel from dripping out of the carb float vent line while being transported in my truck. Coincidence? I can't imagine how any excess fuel could possibly slosh pass the pilot jet and into the engine during transport...and even if it could, it would be such a miniscule amount as to be inconsequential. Maybe there is something else going on by leaving the float bowl full?¿

[This message has been edited by Boit (edited 03-16-2001).]

Thanks yzernie, i used your suggestions and after i put a new plug in it the thing runs AWESOME. i think i've the the procedure down now. This thing is very fun. thanks for all your guy's help.


Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Similar Content

    • By Zack Ailing
      hey guys just picked up a new project bike. Its a 2008 Yz450f with a big bore kit and a stroker crank. The total cc of the engine is now 499. It runs on race gas and will be an absolute monster when shes ready to rip. I will continue to make more videos on the bike so stay tuned Link to the video: 
    • By High On Octane
      2005 YZ450F, Athena Big Bore, Power Bomb, Q4.
      Ok.  Last fall after a decently hot day at the track, I noticed coolant leaking from the weep hole on my water pump after pulling into the pits.  Ordered an Athena re-seal kit, put it all back together and didn't really get a chance to ride it.  3 weeks ago, went out to the track, and after about 20 laps, it started leaking again.  Kept filling it with water to get thru the day, never ran anywhere close to dry or empty, jut a cup or 2 low.  Ordered a Hot Rods re-seal kit with bearing and also ordered a new w/p shaft.  Did it all again and got it back together, ran it, and as soon as it got to temp, it was leaking out of the weep hole again.
      So, what the heck am I missing?  I'm totally stumped on this one.  Is something wrong with my case cover?  Do I need to replace the w/p itself?  I'm feeling like I should've just ponied up for the Boysen in the first place, and now it's biting me in the butt.  Any help or suggestions is greatly appreciated.  Thanks!
    • By Awheeler25u
      Alright guys, my 04 YZ450f runs fine minus some slight backfires when decelerating (need to adjust fuel screw). The other day when I was done checking my valve clearances I changed the oil and filter and put the bike back on the stand, kicked it a few times without the ignition coil in to get some oil flowing got off and noticed a little drip spot on the ground, it was no bigger than a dime so I thought nothing of it. Started the bike with no issues took it for a quick 10-15 min ride, came back to the garage to find out my whole case was soaked with oil and it started pooling in the low spots on the clutch basket side. I cleaned all the oil off and took it out again for 5 mins to try and see where it was coming from, here are my three possible places but nothing directly leads me to believe it’s any of the three either.
      1. Decompression plug area
      2.  Valve cover gasket leak (not really sure because the amount of oil leaking Looks to be a large amount
      3. Oil tank (bad weld or cracked weld somewhere
      what are you guys thinking?
    • By bofar
      Hey guys. I could really use your help diagnosing an issue that came up riding today. Bike is a 2013 YZ450F. Well maintained and haven't had any issues until now. Both the oil and coolant are new and levels are to spec. 
      After riding for about an hour in the sand dunes, I noticed a grinding going on on the right side of the bottom end (from what I could tell). When I looked to see what was going on my kickstarter was vibrating and grinding really loud. This was a different sound than if you engaged the kickstarter while running. It sounded less "clanky" and more "vibrating/grinding" if that makes sense. Grabbing the kickstarter and moving it didn't help the issue.
      When I noticed it, I shut the bike off and gave it a second. Being a few miles deep into the dunes, I had to get it out of there so I started it back up and it seemed fine- no grinding. I headed back to the car and after a few minutes, it came back so I shut it off again, started it back up and nothing. That process happened one or two more times before I made it back to the truck. Seemed to run fine otherwise. 
      Once I got it back to the truck I started it up and tried to pay more attention to what was going on but it wasn't doing it. I did seem to have more of a metal on metal noise coming from the motor. I started and stopped the bike a few times and after the motor stopped there was a distinct metal clank/grinding noise that happened right after the motor shut of for maybe half a second. This doesn't happen every time. 
      I tried doing some research and have seen things that make me think it could be the spring that connects to the kickstarter, or the kickstarter stopper plate- but really I have no idea.
      Seems strange that the issue is off and on.
      Thanks for the help!
    • By Goof331
      Does anyone know if there is any differences between the 2 radiators? Will the yz450fx radiator bolt on a yz450f? What I am wanting to do is wire up a fan to my 2016 yz450f. I know how I am going to do it I just don’t want to use a “universal” fan kit. What I would like to do is get a 450fx radiator and the direct bolt on Trail Tech fan for that radiator to have a good clean look.