'03 YZ450F carb trouble

5 replies to this topic
  • gtilley45

Posted January 17, 2012 - 12:13 PM


I've already tried a search and read through a lot of the posts here and haven't found what I'm looking for so I thought I'd just ask.

I've got an '03 YZ450F that I couldn't get to run right to save my life. I tried everything I could think of including every jetting combo imaginable but it still acted like it was sucking air. After looking closer at my carb, it seemed to be pretty much worn out so we figured that could have been the problem. My mechanic/sponsor was helping me with this, and he suggested putting the carb from his CRF on there so we did and it ran perfectly. So that pretty much made up my mind that I needed a carb...but the '03 YZ carb is reduculously high (as I guess y'all know) and I can't afford one. So my question is, what all year carbs will work on the '03 YZ450F? I know the '03 and '04 carbs have the same part number and that's all any of the dealers around here said they could do was compare part numbers.

  • grayracer513

Posted January 17, 2012 - 01:04 PM


Carbs from an '03-'09 YZ450 will bolt on directly. Those from a CRF450 from the time they started using the hot start cable on top of the carb will work, but they're also bigger.

before you replace it, check the following:
  • Hot start plunger free, has a seal, and is closing
  • Vacuum release plate installed right side up ("square" end down)
  • O-ring in place on the idle mixture screw
  • Pilot jet actually is clear (not just looks clear http://www.thumperta...726#post8021726 )

  • gtilley45

Posted January 17, 2012 - 01:40 PM


I've checked what you mentioned on the hot start. Is the vacuum release plate on the slide? I was told to check that and did. The o-ring is in place on the mixture screw. That was one of the first things I found. I turned the carb sideways to adjust it and saw that it didn't have a mixture screw so I bought an aftermarket one which made it a lot better but still not completely.

Thanks a lot for the advice! I'd love to hear some more.

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  • gtilley45

Posted January 17, 2012 - 01:44 PM


I knew the CRF carb was bigger, but it's a full national level motor so I figured it would be ok. It's actually got a CRF carb on it now and is better but this carb is one I got from a buddy that has a LOT of time on it and isn't in the best shape. So I'm looking around for YZ carbs that are in decent shape.

  • grayracer513

Posted January 17, 2012 - 02:43 PM


So, we're working on a modified engine? Would have been nice to know that to begin with.

  • gtilley45

Posted January 19, 2012 - 03:52 PM


Yes....highly modified. I guess I forgot to mention it because I was basically just wondering what all year carbs would work. I know the tuning of the carb will depend on the mods done and I can handle that I think. The CRF carb my friend has worked like a charm and ran perfectly. So between that and all the other stuff we looked at, I was fairly sure that a good carb would be the ticket.

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