99 yz400f

64 replies to this topic
  • tmeyer37

Posted August 02, 2008 - 09:07 PM


just bought 99 yz400 with some problems already. Well the gas tank is leaking from the upper bolt on the right radiator shroud and from the fuel valve which is easy enough to fix. But this carb sucks. When i bought the bike it barely ran. It has all stock jetting and the fuel mix screw out 3 turns. It runs fine top end but wont idle with out the choke on and is a bear to start. The trouble starting is from the carburation im sure because i used to own a 01 wr250f and never had a problem starting that and my dad had a 98 yz400 and never had a problem with that either. I think the carb is just too gunked up but wanted a second opinion. Also i already did the standard new plastic routine but anybody know of some good dress up parts for it. Im not looking for something crazy just want to make it look clean

  • FlashGordon

Posted August 02, 2008 - 09:29 PM


Can't remember how I had my 99 YZ400F set up exactly before I sold it, but it was the easiest starting bike after jetting it right. Go up two sizes on the pilot jet, and set the pilot screw to 2 turns out. The JD jetting kit was a huge improvement.

  • tmeyer37

Posted August 02, 2008 - 09:34 PM


yea im not sure if i want to rejet it yet i need a new pipe for it cuz it has a white bros and it is too loud. So once i get a new pipe then i will put bigger jets in when i get the new pipe

  • tmeyer37

Posted August 04, 2008 - 12:33 PM


not sure what to do. i cleaned the carb out but still wont run with out choke on

  • 426

Posted August 04, 2008 - 12:52 PM


Before changing parts I would definitively make this bike idle right. Take FlashGordon's advice and start by getting a bigger pilot jet and see what happens...:ride:

  • TooFast

Posted August 04, 2008 - 12:53 PM


your pilot jet and or passage is plugged

  • tmeyer37

Posted August 04, 2008 - 01:01 PM


does anyone know what the yamaha stock setting for the pilot screw is. I have it at three is that too much or not enough. And does turning it out richen or lean the mixture.

  • 426

Posted August 04, 2008 - 01:14 PM


Well... If u turn the pilot screw in, you will increase idle speed. You can try to turning it in or out but if nothing happens, you may want to try changing the pilot jet size, which means replacing the jet by another with a bigger hole in it...

  • 1998YZ400F

Posted August 04, 2008 - 03:41 PM


three might be too much. somewhere around 1 1/2 - 2 turns out is fine. does it bog off idle or anything or just flat wont idle because its too low?

  • grayracer513

Posted August 04, 2008 - 03:46 PM


does anyone know what the yamaha stock setting for the pilot screw is. I have it at three is that too much or not enough. And does turning it out richen or lean the mixture.

Turning it out richens the mixture. Baseline should be somewhere in the 1.5-2 turns out.


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  • tmeyer37

Posted August 05, 2008 - 05:52 PM


So the next question is how interchangable are the parts between the yz400 and say a 426 or 250f. I want to put an aluminum sub frame on my 400 will one from a 426 or 250f fit?

  • 1998YZ400F

Posted August 05, 2008 - 07:57 PM


are all the problems fixed already?

  • tmeyer37

Posted August 06, 2008 - 07:59 PM


no not yet but im pretty sure i just need new jets. The old ones are really oxidized. The bike was sitting for about a year so im getting new jets on friday and hopefully that solves the problem.

  • fshum

Posted December 26, 2009 - 09:21 PM


I have the exact same bike and problem. we put the bke in the garage for a few years and next thing you know i have this prob. i cleaned the carb but it still runs only wit choke on idle. sounds mean when you rev it up. it has a new piston and everything from like 2003. it has to be something simple. im gettin ready to dump this beast in the bay.

  • fshum

Posted December 26, 2009 - 09:23 PM


let me know if you get it runnin'. mine leaks oil out of the shifter seal like crazy.

  • myoung

Posted December 27, 2009 - 09:27 AM


I have the exact same bike and problem. we put the bke in the garage for a few years and next thing you know i have this prob. i cleaned the carb but it still runs only wit choke on idle. sounds mean when you rev it up. it has a new piston and everything from like 2003. it has to be something simple. im gettin ready to dump this beast in the bay.

I just spent a nice chunk of my life dealing with this. There are a ton of threads on this as well. Do a search for 'hanging idle' in all the other model threads as well as the Yamaha threads.

The short story here is it's more than likely somewhere in your pilot circuit. There are a few things that can be wrong, but since yours sat so long, it's probably a clogged jet or passage. You'll probably have to do some more cleaning and possibly get some new parts.

If you can't fix this with the pilot circuit, then check the slide plate(square end down) and seal, check for air leaks and check your throttle cables. These four things are what my searches, and eventual solution, have turned up to be the things that can cause this. My thread is in the DRZ400 section.

Good luck

  • fshum

Posted December 28, 2009 - 09:26 AM


Thanks m young. The carbureator has been air compressed and sprayed and stripped down the pilot circuit is completely clear because air is blowing through it and coming out of the little hole just past the slide. Maybe it is not clean enough I don't know.

We had it running last night again after we completely air compressed the carb (again) just for good measures. it pops and blow flames out the exhaust when you rev it with out the choke.

The original problem with it not starting was that the pilot jet was blocked with green stuff from sitting so long. Now that I cleaned that out it still only runs with the choke.

The guy at zip ty racing told me that it was the pilot circuit (which is what I wish was the problem) , or it is tight intake valves. Well we didn't check the valves cause it was too late but I left it at my friends storage bin and he is gonna check it today. I still don't think that could be the problem though.

This is really my very close friends bike who shared it with me and my brother and he actually wants my brother to have it for sentimental reasons. I just tried to get it running for them. back in 2005 my friend took it out a bunch of times in the sand pits and just hosed it off and put it away dirty. so the carbureator looked pretty bad.

I don't see how it could be tight intake valves but I'll keep you upddated.

  • myoung

Posted December 28, 2009 - 10:26 AM


Try checking the valves, check for air leaks at the connection between the carb and head, check that the throttle cables aren't binding and check anything else someone suggests. If none of that works, have a run through my thread in the DRZ section and see if my solution is what you're dealing with. And just so you know, being able to blow cleaner and air through the passages doesn't meant they're not blocked, as I discovered.

The carb on my DRZ is actually a Yamaha carb, but all the early style slant body FCR's are basically the same inside. After finding my problem, there has already been another guy in the same boat that his ended up being the same problem.

DRZ thread

With all the people struggling with the FCR's hanging idle problem, there really should be a complete, comprehensive FAQ on it in every makes threads.

  • fshum

Posted December 28, 2009 - 11:45 AM


So it really looks like a I need to take the body of the carb apart from the floatbowl side and check that gasket out right? I did not do that yet.

I hope it works because the bike used to run fine, sat for a few years and collected green gunk, and now it won't run. thanks again

Hey how did you end up finding this thread even after you solved your problem? Are you just doing a good deed for all of us suckers out there?

And how do you get those dancing icons? I don't need to be a computer web designer to do that?

I'm gonna try to get this bike runnin' before it ends up for sale as parts on ebay

  • myoung

Posted December 28, 2009 - 12:27 PM


I don't know if that is your problem, but it's worth it to check. My solution is really the last thing you would try as if you break something taking it apart, you're done. You just have to be careful.

If you try it, the wrench you need is a 2mm and I wouldn't use a ball end or long reach allen wrench. Use as short of a wrench as you can, and preferably a brand new one. The long end reaches in, and a crecent wrench on the short end to break it loose. They are very small and very tight with a dab of small fastener lock tite. Whatever you do, don't separate the two outer body pieces, they are epoxied together. Only remove the inside piece the slide goes over. That's what the two screws in the float area hold.

I've been on this forum for a long time and I've mostly hung out in the Yamaha section, that's how I saw this thread. I put my thread in the DRZ section in case it wasn't the carb, but something specific to the DRZ's. I couldn't get the answer I needed so I searched all the makes for this problem. I got quite the FCR education in the process and I started noticing there is a lot of people struggling with this, and some that haven't been able to find a solution.

I knew there had to be something else to look for beyond the typical suggestions. I was lucky to have another carb I could dig into without the fear of ruining it. Now that I have this knowledge, I'm happy to share it. If I had read this thread before I ever knew anything about this problem, I would have had nothing to offer and moved on. But now that I know, anywhere I can help I do.

Besides, I'm unemployed right now and bored. :cheers:

The dancing icons are in the smilies box to the right of where you type your posts. :moon:

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