1999 YZ400F Issues


12 replies to this topic
  • 1999400F

Posted August 23, 2011 - 01:48 PM

#1

ok people, new to the 4-stroke world here! I just bought a 1999 yz400f and i love it...up until now, lol.

Symptoms: High Idle, back firing (stock exhaust), stalling, when wot it boggs down (i need to gradually accelerate), smoking (may be from the sea foam i put in it...:):banghead: i never use that shit, I got talked into it) and top end noise, kind of like a spinning noise (it has hot cams in it from previous owner with less than an hour on them) I heard these engines are noisy so is the spinning sound normal?

The guy I took it to said the carb is fine and may need a top end rebuild. The bike does not lack any power to my knowledge. I can get it to fire up first kick with the choke. Any ideas of what may be going wrong? Any help will be greatly appreciated! thanks!

  • DeeCee

Posted August 23, 2011 - 11:13 PM

#2

Has it developed these symptons recently or has it run like this since you brought it ?

  • BlindLOKI

Posted August 23, 2011 - 11:15 PM

#3

What condition is your air filter in? If it's good you can try to unplug your throttle position sensor (its on the carb) and see if that clears it up... Other than that it could also be in the accelerator pump circuit of the carb but if you guys says its good he checked that I assume... The high idle and stalling is a symptom of either poor timing/map or an air leak. Definately make sure your air filter is in good condition and properly lubed up. Outside of that I really dont know, just thought I'd give you a place to start :)

  • Schpenxel

Posted August 24, 2011 - 07:43 AM

#4

ok people, new to the 4-stroke world here! I just bought a 1999 yz400f and i love it...up until now, lol.

Symptoms: High Idle, back firing (stock exhaust), stalling, when wot it boggs down (i need to gradually accelerate), smoking (may be from the sea foam i put in it...:):banghead: i never use that shit, I got talked into it) and top end noise, kind of like a spinning noise (it has hot cams in it from previous owner with less than an hour on them) I heard these engines are noisy so is the spinning sound normal?

The guy I took it to said the carb is fine and may need a top end rebuild. The bike does not lack any power to my knowledge. I can get it to fire up first kick with the choke. Any ideas of what may be going wrong? Any help will be greatly appreciated! thanks!


Did the symptoms start immediately after the sea-form or just randomly or when you bought it or what??

Have you checked the valve clearances? That's about the first thing to do, regardless of it's past, on any bike that was just purchased. Also check to see how stretched the timing chain is. You may want to go ahead and replace it--If it breaks, you'll spend as much fixing the bike as you probably paid for it lol. Def not fun.

Also, mine idled pretty bad when I had the pilot jet setup wrong. Are you sure nothing is clogged in the carb at all?

  • 1999400F

Posted August 24, 2011 - 08:15 AM

#5

Has it developed these symptons recently or has it run like this since you brought it ?


When purchased it had a high idle with choke on and then wouldn't idle. The guy let it sit for a few months with gas till in it. we had some crazy heat this summer so i figured it evaporated in the bowl leaving deposits and needed a clean. Ran fine when i test rode it, fired right up and was balls fast :)

  • 1999400F

Posted August 24, 2011 - 08:18 AM

#6

Did the symptoms start immediately after the sea-form or just randomly or when you bought it or what??

Have you checked the valve clearances? That's about the first thing to do, regardless of it's past, on any bike that was just purchased. Also check to see how stretched the timing chain is. You may want to go ahead and replace it--If it breaks, you'll spend as much fixing the bike as you probably paid for it lol. Def not fun.

Also, mine idled pretty bad when I had the pilot jet setup wrong. Are you sure nothing is clogged in the carb at all?


He didn't actually check the carb but he test rode it and said my problems were someplace else that he can't fix. I'm assuming he ran out of time and was like "**** it I don't have the time to clean this guys carb for 20 bucks". Haven't checked valve clearances or timing chain-can I do this by just popping off the top of the head?

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  • grayracer513

Posted August 24, 2011 - 11:17 AM

#7

Yes, the cam cover is where you need to go.

You need a manual. If you can't get the download for the '99 to work from either site, try the manual for a 2000 426. Most of what you need will be the same between them. In fact, you may want to download that even if the one for the '99 works right, because the 400 manuals used photos instead of the line drawings in the later ones, and the photos don't always reproduce well.

http://www.yamaha-mo...uals/index.aspx
http://www.yamahaown...ook.com.au/?r=0

On the carb, it's a safe bet that the pilot jet has dried varnish in it:

http://www.thumperta...726#post8021726

  • 1999400F

Posted August 24, 2011 - 11:52 AM

#8

Yes, the cam cover is where you need to go.

You need a manual. If you can't get the download for the '99 to work from either site, try the manual for a 2000 426. Most of what you need will be the same between them. In fact, you may want to download that even if the one for the '99 works right, because the 400 manuals used photos instead of the line drawings in the later ones, and the photos don't always reproduce well.

http://www.yamaha-mo...uals/index.aspx
http://www.yamahaown...ook.com.au/?r=0

On the carb, it's a safe bet that the pilot jet has dried varnish in it:

http://www.thumperta...726#post8021726



Yes, I have a 99 yz400f manual but the drawings are a little hard to depict. maybe I'll download the one with the line drawings. I'll have to mess with it on thursday seeing as the bike is in sanudsky and I'm in Toledo.

  • 1999400F

Posted August 24, 2011 - 12:03 PM

#9

also, they guy just slapped hot cams in the thing-should he have replaced the valves and would there be any clearance issues? also if worse comes to worse can I put a 450 engine on this thing?

  • Schpenxel

Posted August 24, 2011 - 12:04 PM

#10

You have to clearance the valves at least. That usually involves ordering new shims..

If he literally just stuck a new cam in it and didn't check clearances/replace shims to get the clearances in spec, then that could certainly cause some issues. Like I said earlier, you need to check the valve clearances.

  • grayracer513

Posted August 24, 2011 - 12:47 PM

#11

Installing new cams does not require installing new valves, although it does require the clearances be checked and adjusted.

A 450 engine will not directly fit, and frankly, you'd spend more money on doing something like that than on simply replacing the whole bike with something newer.

  • 1999400F

Posted August 24, 2011 - 03:18 PM

#12

You have to clearance the valves at least. That usually involves ordering new shims..

If he literally just stuck a new cam in it and didn't check clearances/replace shims to get the clearances in spec, then that could certainly cause some issues. Like I said earlier, you need to check the valve clearances.


I think thats the first thing i'll do after i try a few other easy fixes to see if that solves it.. thanks guys..will post some results

  • papabru80

Posted October 14, 2012 - 11:19 AM

#13

hey u guys think u coauld help me out? i have a 99' yz400 and am having problems with it that i cant resolve. i bought it and cleaned the carb and now it runs great until it gets hot, after getting hot it will start cutting in and out until i get really on the top end. but it only does it when its hot, afte i warm it up it will run awesome for about 15-20 minutes.
any ideas would be much appreciated! thanks all!





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