1999 Yz400 Will Not Start

Guys I need some help. I am new to the Dirt bike world. I have always run 4 wheelers and started running dirtbikes this year because I got my son a ttr90 last year . I got this nice used 99 YZ400F this summer. It run good for a few months now it will not start for nothin. I am in Tennessee.

I have changed the spark plug

Change the Air Filter.

It has a Handle bar Hot Start on it.

I have no Idea why it will not start. I bought a factory spark plug I asked if it was pregapped and the parts guy said "yes". Is that right?

Does any one have any other suggestions?

I have read some of the forums and notice something about Jetting. Would I need to rejett after a plug change?

From some internet research it seems these older 90 model yamahas are known for hard starts.

Any help or suggestions would be great.


If the spark plug is new you will not have to rejet. And the spark plugs do come from factory pregapped. Make sure you do not touch the throttle at all. Even when it is off it will still flood it. When I first got my 99 it was hard to start and I just heard from everyone else what to do and did what worked best for me. My bike is bone stock and this is what I do:

1. With gas turned on, and cold start pulled out(black knob). Kick, with decomp lever in, about 3 times.

2. Let decomp lever out. Kick until it stops because of compression(it may take more take once)

3. Take kick start all the way to top. Pull in decomp lever and very slowly push kick starter so the piston is at top-dead-center( about 1 to 2 inches of movement of the end of the kick starter)

4. Bring kick starter to the very top and mak sure it grabs the last click.

5. Let go of decomp lever, and hand off throttle, KICK LIKE HELL!

6. If it doesn't fire up repeat 2-5.

That has worked for me every time. You just got to feel and imagine the position of the piston inside. I usually just do 2-5. If this does not work do a search on starting the 400.

There is so many things that could be causing your hard starting.

Valves out of adjustment will cause hard starting.

It may need to be re-ringed if it never has before.

If the timing chain has never been replaced it could of jumped timing. There was a rash of timing chain failers last year on the 99's. Seems they reached the end of there life at around the 4 year mark. Bad tensioner could also cause jumed timing.

Completely disasemble the carb and thourgly clean it.

Check all the electrical conections and make sure that they are clean and dry. Squirt some di-electric grease into them.

Ok a few dumb questions. When you slowly kick it thru the stroke, when the piston hits TDC the kick starter stops form the compression. You then need the compression release to bump it past. If you can kick it past TDC without the compression release you may have valve isues or need re-ringing.

What I always do it eleminate the possible causes and whatever is left has got to be the problem. You need gas spark and compression. In order to get compression you need good rings, valves sealing and shimmed properly, Cams timed corect.

Good luck. The more detailed info on what you have checked the more we can help.

Yzman400 gives great advice here.

My '99 YZ400 just had a similiar thing happen to it. It seemed to be running fine and then out of nowhere it just stopped running. It wouldn't start for anything. My friend diagnosed it as being related to the compression rings. He did this by the method that yzman400 stated which is the ability to kick the bike past TDC without using the decompression lever. For me anyway, it wasn't just the fact that you could kick it past TDC, but more the fact that you could do it easily.

I just got the bike back yesterday. I can't wait to take it out to see how much better it runs now!

Very good points these guys made. But again its a little hard to diagnose over cyberspace without accutually seeing it. It could be one of many things or a combination. Maybe you could find someone in your area.

Thanks everyone. These are great suggestions.

And No I can not kick it without using the compression lever. I am going to try these and let you know how it goes.

How do I know if My trhottle screw is set right. Is there a mark on where it starts. I have twisted it several times and cant seem to turn enough all the way - one way to see where itstarts.

Any ideas?

You lost me with the throttle screw. Are you talking about the idle screw on the lh bottom side of the carb (black knob) or the fuel screw in the bottom of the carb float bowl?

Sounds like you have compression. Turn on the gas and tip the bike over on its side and look for gas spewing out of the vent tubes. That will tell ya if gas is getting into the carb.

Hey what is your temp around there right now? These bikes can be a bear to start in cold temps around say 30 deg and below. Rejeting is usually needed to get them running in the cold winter months.

Have you checked for spark? Take the plug out, plug it into the plug wire and rest the plug against something metal and kick to check for spark.

Yes the black knob on the lower right side pretty close to the gas on/off knob.

Its been in the 20's and thirtys'with a windchill in the 10's

so it could be a jetting issue if you say it usually needs rejetting in colder temps.

Any good sites on talking about "How to rejett your bike"

Thanks for the tips


All the advise given are great, My advise is make a list of everything here you have not tried and go down it one at a time.

Another suggestion I did not see is the Kill Switch, Take the kill switch off, this may be defective and causing no spark, Make sure you are getting spark as well.

As far as starting goes, follow the drill, live it love it sleep with it and never never ever let anyone twist tat throttle when the bike is not running

The Drill

Welcome to TT :cry:

Ok guys,

So I tried starting it again and nogo.

I tried turning it on its side and gas came out of the vents.

I do get a loud single pop once or twice. What does this mean?

Still not sure if I got the idle scree correct.

That means you have flooded it. Kick it over 20 times while holding the decompression lever then let it go. Find TDC then pull the decom lever a 1/4 of an inch. Kick it about an inch. Let go of lever bring kickstarter to the top and kick as hard as you can. Do not touch the throttle. Do this with the choke and the hot start off. Make sure you have the idle set perfect too. Other wise it will not start.

Ok cool me a newbie but what does TDC stand for?

TDC "top dead center" Correct ?

yep top dead center

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