400f carb bored?

8 replies to this topic
  • Buzzy613

Posted March 13, 2016 - 04:29 PM


I've still been tracing the whole carb issue on this bike but this caught my eye today, is seems like it was bored to an oblong shape, I will mic it tomorrow. But this doesn't seem factory to me

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  • Buzzy613

Posted March 13, 2016 - 04:39 PM


I just measured it it measures 41mm on the vertical axis and mid way up on the horizontal it measures 39mm so with this home made bore job on stock jetting would cause it to spit sputter and pop like it is now? Also after this discovery I feel like it would be wise to go to a newer 450 carb correct?

Edited by Buzzy613, March 13, 2016 - 04:47 PM.

  • grayracer513

Posted March 14, 2016 - 06:42 AM


It would be anyway.  The bore likely has nothing to do with how it's running, though.  The old FCR's get to be a huge pain in the butt when they get worn and/or develop internal problems.

  • Buzzy613

Posted March 14, 2016 - 07:35 AM


I found an 03 450 carb throttle cable and hotstart, I know in multiple forums you stated 05+ but I'm unsure if the 03 will help much like the 05+

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  • grayracer513

Posted March 14, 2016 - 08:33 AM


The '03 will work, and quite a bit better than the original.  The downside to the '03-'04 carbs is that they don't have a leak jet, which takes one tuning tool off the table, but that's not a big deal, really.

  • Buzzy613

Posted March 14, 2016 - 08:55 AM


Alright thank you so much, I know this question gets beat to death but past threads only have so much information

  • Buzzy613

Posted March 22, 2016 - 02:53 AM


Would a 40mm fcr from a crf work if I swaped the needle out for the stock yz450f? And tool the time to jet it?

  • grayracer513

Posted March 22, 2016 - 07:12 AM


Probably, but I don't know about the throttle cables, nor whether the main air jet and main nozzles are the same.

  • Buzzy613

Posted March 22, 2016 - 10:48 AM


Well I thinknits found my issue the vacuum release plate has a big hairline crack in it, so im going to order a new one and a rebuild kit for this carb, since there is no 450 carbs anywhere on ebay

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