2007 YZ450 carb on 1999 WR400F Questions

Hey guys, lost my old account info as it's been so long sense I got on the forums. I recently picked up a plated yammy 99 wr400f, and I'm, having some carb issues. Everything is perfect 1-1/8th throttle, and near half throttle I get awful stuttering that makes it jump untill it clears it, and then im back into the really torque range. Sounds like it's bubbling, and just running like crap in that one spot. I bought a new needle, and cleaned all the jets and it still does it. I';m running jets 186/60/45. So pretty much stock. IT has a FMF power bomb header and exhaust.  instead of fixing my issue, i'm looking at a pretty nice used 2007 yamaha yz450f Carb with the throttle and everything on fleabay.  Would it be a direct fit, and only a few minor adjustments? i've searched the forums, and i've seen mixed opinions on the switch and compatibility. If I could get some info on it for sure either way, i'll bite the bullet and buy the carb. , The bike runs perfect, starts first kick despite it being 30 degrees in the morning. Thanks for the help guys, I really appreciate it. Hope this is in the right section   :ride:

Bought a 2007 yz450 carb on the bay for 180ish shipped, a little steep but i don't mind considering it's a newer year and i'm itching to get riding again. Hopefully it'll bolt up and i'll only have to ajust a few things. will probably buy a rebuild and some spare jets. will update when i get it in.

Jetting should be 170m 45p, ncvs or richer

NCVS is entirely the wrong needle for an '07 YZ450 carb. 


The '07 carb is a near direct fit on your WR400F.  The first point of interference is that the carb is a little bit shorter front to back than the original, so the air boot needs to be stretched slightly to reach.  The simplest way to accomplish that is to clamp the air boot to the carb first, then push the carb forward into the mounting sleeve. 


The second thing to be aware of is that the 450 carbs all have a cable operated hot start, whereas yours is an external system.  Here, you have two choices.  The first and best choice is to be sure you buy the carb with as much of the original hot start as you can get from the seller, including the plunger, cable, attaching nut, spring, lever, etc., if possible.  Then, you simply pull the hose and valve off of the old system and cap off the ports.


Alternately, install the hot start plunger, seal, spring and nut in the carb, plug the hole in the top of the nut, and use your old hot start set up. 


Other than that, you need the throttle cable set for the 450 as well, but your throttle tube will work.


Usually, stone stock YZ450 jetting works well on the older bikes, but if it's been tinkered with, the jetting for sea level to close to 4000 feet should be a 165-168 main, 45 pilot, and the stock NFLR needle in the 4th groove.

Thanks a bunch for the info grey, I bought the carb with the full throttle cable assembly and grip that was on it. So it should be everything including the hotstart. I'm not sure if I can post a link to the one I bought on eBay, So I won't just yet. Just got some alpinestars sp8's in the mail from Amazon, got them for 1.80 shipped. There was a price mistake and they were listed 45$, and I had a gift card for 44 bucks. So I'm pretty happy. Had them before but had sold them with my last bike.

Hey guys, I threw the carb on the bike, and put the screw two turns out, and I cant get it to start for the life of me. i'm about to take it all back off, have any tips? ill get the jetting info shortly

Hey, got an update. Had to clean the carb a little, the float valve was stuck closed. Had a new one I threw on, and cleaned it. Started first kick. I all my carb issues are solved and power is on tap even more so it seems. Really looking forward to tomorrow to go for some hooliganizm.

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