03 YZ450 Runs Bad !!

14 replies to this topic
  • 6951

Posted March 29, 2005 - 06:32 PM


I put a top end in (piston ,rings ,wrist pin clipsetc) The valve clearances were right within the spec in the manual. The hot start plunger was stuck in the Carb I had to break one of the little ears off to get it out, I bought a new one and a seal cleaned the bore out it slides in out nicely.

I start it up for the first time since the rebuild second kick it is idling really high with the choke on let it warm up crack the throttle great response but as soon as you let off the throttle it bangs or snaps it won't idle or idles erratic Pull the hot start and nothing while it is running. When you used to pull the hot start the idle would pick up not any more !!!!

Double checked the cam timing it is correct
Three sizes richer on the main and the pilot nothing changed

Any Ideas?

  • fatnugget

Posted March 29, 2005 - 06:51 PM


I'm not an expert but it sounds like you have an air leak somewhere in the carb or intake tract. I know when I lost the air screw out of my carb it ran like crap. You could try an old trick from working on cars to help find an air leak. Start the bike and spray some starting fluid on the carb and intake. If it idles higher or speeds up you have a leak to track down.

  • 6951

Posted March 29, 2005 - 06:53 PM


Great Idea and thanks but I tried that all ready :naughty: No Leaks !!!!!!

  • yzf450jack

Posted March 29, 2005 - 08:00 PM


Did you have your slide out and put the black plate upsidedown It's a common mistake the flat side is down :naughty:

  • 6951

Posted March 29, 2005 - 08:07 PM


I will Double Check !!! Thanks

Keep The Tips Coming Please This is Driving me Nuts !!!!!!

  • ovrrdrive

Posted March 30, 2005 - 01:47 AM


Are you sure the hot start plunger is working right?

I put mine in the other night and got it stuck somehow and had the same problem as you. It was so lean it ran a little hot and had a very irregular idle.

I reset the hot start and all is fine.

  • 6951

Posted March 30, 2005 - 04:20 AM


At this point I am not really sure of anything !!!!

I checked the hot start plunger a couple of times, it moves free with the cable and I even unhooked the cable measured the depth of the bore and the plunger overall length and it is bottoming out in the bore. I will double check it Thanks

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  • Ga426owner

Posted March 30, 2005 - 06:46 AM


I had similar issue when I stripped out the threads on the plastic Hotstart plunger nut that screws into the top of the carb - I bent the "ears" you are talking about and lost the spring that is part of that assembly -
For me I replaced the spring and bought the ZipTy metal plunger nut - this cleaned up the issue for me.

  • MotoGoalie

Posted March 30, 2005 - 07:08 AM


I think your hot start plunger is permanently stuck open. I had the SAME problem.

  • 6951

Posted March 30, 2005 - 08:15 AM


What I did with the Plunger is I removed the cable and the spring and slid the plunger all the way into the bore, then started it up same thing !!!! That should like that ?

  • 6951

Posted March 30, 2005 - 10:15 AM


Nobody has anymore Ideas ? :naughty:

  • Kramer

Posted March 30, 2005 - 11:15 AM


It may be the auto de-comp is hung up
keeping the one valve open.

  • 6951

Posted March 30, 2005 - 12:42 PM


Never thought of that I will check it !!!!!

  • 6951

Posted March 30, 2005 - 05:42 PM


Did you have your slide out and put the black plate upsidedown It's a common mistake the flat side is down :naughty:

You Were correct I had that Plate in Upside down !!!! Thanks For The Tip :naughty:

  • Satch0922

Posted March 30, 2005 - 06:01 PM



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