WR 400 Difficult to Make Run

14 replies to this topic
  • amr126

Posted February 14, 2011 - 04:06 PM


Hey guys, my uncle gave me his 2000 WR400 and I'm simply trying to get it going so my brother has a dual sport to ride. The initial problem when we recieved the bike was that is was very difficult to start, and once started would only run with the choke on. Since then I replaced the top end, and completely disassembled the carb, soaked it overnight in Yamalube carb dip, checked everything and replaced all diaphragms and seals, yet the same problem exists. If I'm lucky to get the bike running, it is only with the idle set high and the choke on. Also, when I replaced the top end I removed all valves and cleaned them, checked them, and replaced the seals. Please help...

  • alfie

Posted February 14, 2011 - 04:11 PM


It maybe worth putting in a new pilot jet and try again, are you also sure that all the valves are in spec.

  • amr126

Posted February 14, 2011 - 09:28 PM


Thanks for the input but I have already tried both of those. Does this sound like an air leak possibly? Could the hot start not be functioning correctly?

  • YamaLink

Posted February 15, 2011 - 02:17 PM


Where is the fuelscrew set at?
Then consider pilot and needle position.

  • amr126

Posted February 15, 2011 - 06:23 PM


I set the pilot screw at 1.5 turns out, a new zip-ty racing unit. There is a new 45 pilot in there too. It definitely sounds like the pilot circuit, but I've gone through every part of it.

  • Kawidad

Posted February 16, 2011 - 08:11 AM


If it still has the octopus still attached, maybe you could try capping it to see if that makes a difference. It could be an air leak. Also, how did the carb look when you took it apart? The FCR carbs are famous for wearing out quickly.

  • amr126

Posted February 16, 2011 - 11:45 AM


Yeah I'll try to disconnect the tps and see if that helps. When I tore it apart, everything looked pretty good. What wears out? I checked the slide and the wear plate looked fine. Besides that is there any parts that are notorious for wear? Is the pilot circuit the only thing needed for normal idling? Thanks for the replys.

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  • amr126

Posted February 16, 2011 - 01:17 PM


So I unplugged the tps and it fires up pretty much first kick now on the choke. But when I turn the choke off, the idle falls drastically. The bike also responds fine to throwing revs with the choke pulled out, but with it in the bike will practically die at a slight stab of the throttle. Anything below a quarter throttle the bike with the choke in hardly runs. I know this all sounds very much like the pilot circuit, but I've gone through it with a fine toothed comb, replacing and cleaning all sections and associated parts that have to do with it. These problems have not improved with completely cleaning the carb and replacing all the parts. Does the wear plate on the slide make a large difference as described above? I'm I missing an adjustment or looking in the wrong place?

  • miweber929

Posted February 17, 2011 - 04:12 AM


Is the idle set real low? Too low to run? Sounds simple but if you've done EVERYTHING else and you're 100% sure you have everything back together right (see other running poor threads about putting the slide in backwards) and have replaced the pilot, not just cleaned it, look at that.

If you hold the throttle slightly open and flip tge choke off, will it still run? Then it's idle speed. Take the carb off, and make sure carb cleaner dqurts from every mook and cranny or you're dead for sure.

  • amr126

Posted February 17, 2011 - 01:07 PM


It will still run if the throttle is slowly applied with the choke off, just very poorly. The idle is definitely set high, since with choke on the bike runs at about 3500 rpms. Adjusting the idle higher with no choke yields no response by the engine, once again unless the choke is on. That is why I'm wondering if an air leak may be plausible.

  • amr126

Posted February 18, 2011 - 07:22 PM


Anyone else? Don't be afraid to have an alternative answer than already mentioned...I use this forum when I need a fresh idea.

  • cor300mx

Posted February 20, 2011 - 10:01 AM


I just got myself the same bike. We had to rebuild the top end, and he showed me the cam gear had slipped a little causing the cam lobe timing to be off. Even though the E and I were perfectly in line, looking at the back the lobes were not in the right position. The bike would never run properly no matter what!

  • groovy2

Posted September 17, 2011 - 05:37 PM


Read this about Hard Starting WR
http://www.thumperta...ght=wr400 start

  • clodeb

Posted October 03, 2011 - 09:54 AM


got the same problem on my '99,i try everything and finaly solve it by changing the whole carb for a yz 2008 i foung cheap on ebay and it work like a charm....night and day without any jetting change...stock yz jetting...nice brown color plug and finally i have a IDLLE!

  • amr126

Posted October 04, 2011 - 05:13 AM


Yeah man I had the same story with my XR650L. Switched carbs and viola, the bike ran fine. Those passages are so small I think nearly invisible damage can destroy a carb.


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