yz400f carb question

4 replies to this topic
  • Cavi

Posted May 01, 2009 - 05:19 PM


okay, my 400, I bought it and it did not run worth a D@@@, cleaned carb and it ran but did not idle well, had to leave idle high so it hung. Tore engine apart and full rebuild, including hotcams. The shop started it up and it still will not idle. They are going to tear into the carb again.
My question, will a carb off a yz450 fit the 400, is that the easyiest fix? I mean I have seen a few on ebay for 200, so it seems not too expensive compared to the nightmare this has been so far

  • gbalias

Posted May 01, 2009 - 05:41 PM


if it wont idle, youre having issues with the pilot circuit. if you change to a later carb, youll need to block off the nipple in the intake side of the head that goes to the hot start knob.

to me, the easiest fix is to jet it properly. if you put in another carb thats not jetted, youre back at square one.

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  • grayracer513

Posted May 01, 2009 - 07:54 PM


With the 400, be sure the Hot Start valve assembly is operating properly. It must open and completely close, and the hose have no leaks.

  • Cavi

Posted May 01, 2009 - 09:39 PM


Can I temporarily block off the hot start to test?

  • grayracer513

Posted May 02, 2009 - 07:16 AM


Yes. either cap the nipple at the intake stub, or remove the valve and plug the line.

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