99 yz400f


64 replies to this topic
  • myoung

Posted February 14, 2010 - 12:18 PM

#61

If your early, slant body FCR is badly worn in the slide, or the A/P circuit is clogged beyond repair, or there is a part that can't be replaced/repaired, or too many expensive parts that need to be replaced, then just replace the whole thing. If it just needs a good cleaning and a few cheap parts replaced, you will not save any money by replacing the whole carb. However, you can get an upgrade by replacing an old FCR with a '00 and later FCR-MX. There are many design changes that are a big improvement over the old FCR.

You don't need to spend a fortune either, unless you just have to have a new carb to replace it. In that case, the Edelbrock might be the cheapest route, but still not the best. There are a ton of '00 and later FCR-MX carbs on Ebay and various classifieds for less than $200, some with next to no hours from brand new, parted out bikes. You may have to buy some other parts depending on the carb you buy, throttle cables, intake boot and remote hot start for example.

Another bonus, pretty much every manufacturer uses them, so if you found the smoking deal on a Honda or KTM carb it could be made to work on a Yamaha, and vice versa. There may be some differences, but if you're replacing an old style FCR, you're already in the process of adapting anyway, so you could do whatever you need to do to get any brand's FCR-MX to work.

There are different sizes that you would have to pay attention to with the FCR-MX, most of the larger bikes use a 39mm, but some are 40 or 41 and the 250F's use a 37. There are differences with the throttle cables, air horn diameters and lengths and the change from a mounted hot-start to a remote hot-start button. There are some other small differences that are manufacturer specific to address one thing or another like Honda's different design on their A/P diaphram.

My advice is to stay on course with a carb the manufacturers use. The FCR's have proven themselves as the best carb for our purpose. I've read a lot of good and bad things about the Edelbrocks and quite frankly, don't know that I would spend that much on one just to try it. The only bad things I hear on FCR's is the frustration when they clog, which an Edelbrock will do as well.

  • fshum

Posted February 15, 2010 - 08:12 AM

#62

valid points. thanks.

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  • Archineer

Posted February 16, 2010 - 02:23 PM

#63

Try 2# bigger pilot jet. I have a 99YZ400 runs perfect, starts easy, has a zillion hours on it. I'll try to find my jetting specs for you this weekend. BUT... my buddy's 01 WR250 had the exact same symptoms this past fall. I did everything - checked valves, cleaned and went through the whole carb. Then another buddy suggested a bigger pilot and viola the thing totally came to life. Runs perfect, starts fine. Went back to 2 turns out on fuel screw. Not sure if we damaged the original pilot cleaning it or what cuz it seems like it still should have run OK with only a slightly smaller jet, but for $4 it's definitely worth a try before going the $$ route.

  • fshum

Posted February 17, 2010 - 03:31 PM

#64

Try 2# bigger pilot jet. I have a 99YZ400 runs perfect, starts easy, has a zillion hours on it. I'll try to find my jetting specs for you this weekend. BUT... my buddy's 01 WR250 had the exact same symptoms this past fall. I did everything - checked valves, cleaned and went through the whole carb. Then another buddy suggested a bigger pilot and viola the thing totally came to life. Runs perfect, starts fine. Went back to 2 turns out on fuel screw. Not sure if we damaged the original pilot cleaning it or what cuz it seems like it still should have run OK with only a slightly smaller jet, but for $4 it's definitely worth a try before going the $$ route.


dude I totally went through all that. you have to read this thread from page 1. I put on a kx450 carb with new cables the bike runs awesome.
For some reason if you leave an old dirty FCR carb on for like ten years it gets real clogged inside and you can't even clean it out. you just replace it. if I had just a dirty pilot I would have never spent hours on this website. I hope no one ever has to deal with the frustration I went through.

  • myoung

Posted February 17, 2010 - 05:41 PM

#65

dude I totally went through all that. you have to read this thread from page 1. I put on a kx450 carb with new cables the bike runs awesome.
For some reason if you leave an old dirty FCR carb on for like ten years it gets real clogged inside and you can't even clean it out. you just replace it. if I had just a dirty pilot I would have never spent hours on this website. I hope no one ever has to deal with the frustration I went through.



LOL!

Yeah, been there, done that.

What did you do with the old one?





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