NEW YZ400 Owner Needing some help!!

Ok I have browsed and searched alot of threads on this bike and my problems... Long story short I got this 99 yz400f not running at a good deal so I took it going on its looks(which is a big No No for me)just because of its shape as you can tell in the pics. I cleaned the carb and the tank. Tank was full of sludge varnish type stuff. The carb wasnt as bad but was bad enough. I gave it a good cleaning and put it back on and got her to run, sounds good with no smoke,nosies,or sounds. My problem now is it is not running worth a crap. My symptoms included the first time I rode it that it was running only with the choke on and very badly at that. I got back online and see that it is running rich(according to what I have come up with on here. I adjusted the mixture screw out a few turns(ya i know,to much) It would run without the choke and even halfway idle at times but my pipe got extremely hot and I guess causing it to overheat and boil antifreeze at 30 degrees and I know its something in the carb causing this. I have also read exhaust leaks will cause this and I will check that also but it will also fall on its face when you gas on it. I am thinking it is starving for fuel and in turn causing it to overheat??? Am I going in the right direction?? Should I try moving my clip one notch down as I have read on here earlier?? Can someone please help a newbie to the 4-strokes. I just come off the 86 cr500. Theres not near as much torque but is very manageable compared to the 2smoke 500. I am very please in the bike I just wanna fix it :smirk: Please Help



FYI these bikes overheat much quicker than a 2 stroke. Some facts that you need to know about all the YZ four strokes from 98 and up.

-These bikes will overheat at idle at around the 2 minute mark, most people think this is a problem but it's normal. You need to keep the bike moving.

-The header on these bikes will glow cherry red when the bike is at idle or running hard, again this is normal.

-Exhaust leaks will not overheat a bike, they will give you popping and cracking from the silencer when it's running though.

Your problems sound almost all carb related, you're going to need to clean it better. I would use a 50/50 pinesol solution with the carb fully stripped and leave it in there overnight.

I would buy all new jets, and not try and clean them, they are inexpensive.

I would clean out the petcock, make sure that it is not plugged up with crap in the screen.

Start there.

I second what brentn said.

Thanks for the tips. I knew they would get hot but didnt know they would get red hot like that....It worrys me because it has a whole new topend on it and for it to get hott like that worrys me... When i got the bike the carb was took apart because the accelerator pump was litterlay rotted. He gave me a replacement but I am still having running issues...I am going to clean the carb good on it today and get a new plug here a little later, I am hoping I did good on the bike for 1000 dollars cash considering its condition. Almost everything on it is mint and I have always been more than averagely poor lol so this falls right in to my category of a nice bike...I live in BFE so getting to a parts place of anykind will take me a hour or so. I havent got the cash to drop for a new rebuild kit for it as bad as I wish I did. I also do all my work myself so this place is a godsent heaven. Thanks everyone and please wish me luck.:smirk:

  • "Runs only with the choke" means that it is LEAN, not rich.
  • Backing the pilot screw out on an FCR carb makes the mixture RICHER, not leaner.
  • The bike, when running perfectly and standing still in neutral will turn the header a dull red visible in twilight within 45 seconds, and boil coolant in under 90 seconds. They like to be moving.

So, with that, regardless of the fact that you say you cleaned the carb, your pilot jet is restricted, probably by a film of dried varnish. This may require you to use a piece of fine wire or a #80 drill bit inserted backward through the jet orifice to clear it. Sometimes, such heavy handed means of cleaning can ruin the jet though. An ultrasonic cleaner may be what's needed.

OK I got it running half @ssed decent,then I get out testing it and was in nutreul when i heard whaat sounded like a chain pop and bam my rear wheel locked down, I can get it going backwards and then it will go forward a little before it locks up again....What could it be. I assuming I have been got when I bought this bike. Anyone know what to look for? I am assuming it is in my trans because it will kick over and run but locked up

You can start the engine, but the bike is locked up?

Can you start and run in neutral, or do you have to pull the clutch in?

Sorry I was not more specific, The back wheel is what locks up like the trans is in a bind. But with the rear wheel locked it does still run so it is not a motor issue but I think a trans issue I just dont know what. Was at a idle in nuetral going down my driveway when the wheell locked up

In that case, assuming it isn't the wheel or brake, it's a problem with the output shaft, or 4th or 5th gears. The rest of the trans turns while at idle in neutral.

I am assuming its probably a sheared piece of metal binding the sproket gear as you were saying. I cant afford to take it to a shop at all but I assume it would make it cheaper if I take the motor out and everything I can do at home to save labor hours ....Do they make a transmission rebuild kit or what exactly will I need to overhaul the transmission?I have saw gear sets on ebay around 150$ and I am sure it will need a entire gasket kit for the engine. Thanks for any heads up on what to look for?? Thanks Rick

You won't know what's wrong until you get it opened up. Gears usually run around $25 each, and the trans bearings are about the same. Replacing all four bearings and the main bearings is a good idea, but the gears need only be replaced as needed. No kits that I know of.

That is good advice and I thank you for that...Anything else you would do while in there on a very strict budget or is there anything else I should repair?? Do you think there maybe a bearing in there on the drive shaft that comes out the side or more than likely a broken gear if you had to guess...Thanks Rick...This is a real bummer for me as tickled as i was with it when i got it...Anyone have the parts I would need??


I had a 98, threw a gear thru the case, cost like $1500.00 Canadian to repair it, had the case welded and parts replaced, as for the "Cherry Glow" normal, hot a F$%K! good luck with the repairs

After the repairs oil change was usually every 6-8 hrs of saddle time only ran syn, till I sold it, other than that regular oil changes and it kept a perma grind on my face while riding!!

Yea I studied the bike before i bought it but I guess not good enough. Its a very clean bike and almost every piece of it is mint so I thought it would be a good bike(the newst one I have had anyway) Tags that sucks it damaged your case...I hope like he!! I didnt damage it or anything else in there. I hope things work out because I have to get it fixed or else wont see a fraction of the money back Thanks everyone...

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