98 Yz400f Idles Briefly Then Dies, Help!!!

hey, it's the new guy again. the 98 yz400f i just bought is acting up. when i test rode it, it ran okay, but the throttle was sticking. i talked to the stealership about fixing it, and they said no problem. i went and picked it up, brought it home, and when i rode it, i noticed it wouldn't idle. at least not for very long. i drained the tank and carb, andfilled it with premium. if it's cold, i'll choke it, ()it takes a couple of kicks,) let it run a couple of minutes, turn the choke off, and give it hell. when i come to a stop, or pull the clutch in, it will run for about a minute, then it dies. it won't restart without pulling the hot start out( i am assuming that is what the other knob below the choke is called?) if i pull it out, it starts on the first kick. it will run for a minute (give or take) then dies again. i can keep it running by staying on the throttle, or by pulling out that lower knob. it acts as if it is running out of gas after a minute or so, but i don't see how it could, because it always starts right back up on the first kick,(as long as i pull out the knob.) and to add to the confusion, sometimes it will die almost immediately after letting off the throttle. but wait there's more! maybe. does anyone know at what RPM this bike redlines, because it seems like the rev limiter is hitting way early. i ask this because if it redlines way up there, then it is also cutting out at a higher rpm. it seems to do this much earlier than my ktm 520 did. that's why i thought maybe it was cutting out. if anyone knows anything, PLEASE HELP!!!!!!!

If I had to guess I would say that you have carb issues. Id say start by taking the carb apart and cleaning everything (carb cleaner and compressd air). Check the jetting against the book to get an idea were you are at. Check the fuel screw position. Maybe it is in too far. Lube the cables and clean the throtte housing. then try it again to see what happens.

Also try a new plug. These bikes are very sensitive to plugs. If you dont have the starting drill down it is very easy to kill a plug.

Thats what my bike did this past weekend until I put a new plug in it.

I had a heck of a time getting back outa da woods to the truck where the tools/plug was. Man, was my leg ever tired from kicking the thing over after it died again and again and again.

That would be my first try if I were you. :)


i just bought the bike,and i don't have the manual yet. what plug am i looking for???

The spark plug :)

It will require removal of some plastic tank, etc. but I bet thats you problem.


i know it's the spark plug, i mean what is the part no. of the replacement plug? thanx

LOL!! :)

You will have to forgive me. I am surely over the limit on my sudafed dose.

I could only respond with 426 plugs, I know they are different for the 400.


Spark plug is a NGK CR8E I believe. That is what my 99 yz400 takes.

thanx for all the info guys!!! for those of you who have not posted a reply yet, keep 'em coming, incase i am at a standstill. anybody got any info about the rev limiter and top RPM of this bike??

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