98 yz won't start

5 replies to this topic
  • brwnelky

Posted October 17, 2010 - 07:11 PM


I have a 1998 yz400 I bought a week or so ago. I rode it to storage went the next weekend it ran but the throttle was sticking open. Took the carb off there was a screw that backed out and was rubbing where the cables go. Tightened sprayed the carb out with some cleaner and played with it some. It still sticks a little bit but seems fine. Put it all back together and it won't start.

I'm obviously not too familiar with the bike but I pulled the plug there was a little bit of carbon on it but nothing crazy. Checked spark it was there but seemed a little weak. Also the hot start button or choke whatever it is won't stay out when you pull it I have to hold it.

It has the bottom end, trans, and stator set up from a wr with a yz top end. The guy I bought it from had receipts from the recent engine rebuild. He said it was in storage for about a year and he took the carb and cleaned it when he pulled it out to sell.

Any ideas?

  • grayracer513

Posted October 17, 2010 - 07:44 PM


Did he have it running less than two weeks ago? Did you see/hear it run before you bought it?

  • brwnelky

Posted October 17, 2010 - 08:39 PM


He said he had shown it to a few people before me (of course) then I went and check it out. We met about 5 minutes from his house he rode it there I checked it out rode it around for a few minutes. Then went back the next day rode it to the storage place which is 20-30 minutes away.

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  • grayracer513

Posted October 17, 2010 - 09:00 PM


Try a fresh plug. The YZ400/426 is touchy about plugs and fouls them easily if run to less than full operating temperature before being shut off.

Then be sure you are using the correct procedure to start it:



Once it's running and warmed up, be sure the idle mixture is trimmed out right:


...they're touchy about that, too.

  • brwnelky

Posted October 20, 2010 - 08:57 AM


First of all thank you very much, I've noticed you can pretty much answer any question anyone has. I'll probably be needing your help again.

Spark plug worked. Started second kick. I've pretty much got the procedure down, my dad had a 2000 wr450 I rode a couple times.

I do need to read up on carb adjustment though. It runs great, scary power but it won't idle at all. I don't have a hot start knob at all just choke and that won't stay out on it's own. But letting it warm up even riding it around you have to hold the throttle open. It backfires/pops on decel but I'm not sure how much is normal. Time to get my learn on. Thanks again

  • grayracer513

Posted October 20, 2010 - 09:04 AM


The idle speed knob is a black knob on the left side front corner of the float bowl. Screw it in to increase the idle speed.

The hot start on the 400 was bolted to the frame near the air boot and ran a hose from there to the intake port on the head. If the hose isn't there, be sure the vacuum port on the intake is plugged.

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