99 YZ400F - Leaking Carb + Hard to start


14 replies to this topic
  • Bethlehem

Posted July 12, 2014 - 01:25 PM

#1

 A couple of days ago I bought a 1999 YZ400F. It has a bad gas leak from somewhere in the carb and I can't get it started. I watched the guy who sold it to me start it about ten times on the first kick so I know it's my technique. But I'm sure the carb leak isn't helping. Is there a list of things I should check, in order of likleyhood, to figure out this leak? Unfortunately this carb is way more complicated than I'm used to so It would have to be something simple for me to tackle it myself. - I had a guy tell me to get it started then run a bottle of carb/fuel injector cleaner through a tank of gas to clean it out.

 

 I have found instructions online for how to start this bike but they vary quite a lot. I don't really understand what they mean when they say to clear it out. I thought kicking it a bunch of times would flood it. Thanks for any help. I did some searches but I'm such a newbie that some of the dialogue was over my head.



  • 90atk

Posted July 13, 2014 - 07:01 AM

#2

id start by trying to see or feel where the gas is leaking out of. i also dont understand what clear it out means. maybe thats for when the bike gets flooded?



  • BBrown626

Posted July 13, 2014 - 03:42 PM

#3

Is it leaking out through one of the tubes or from a gasket?

If leaking froma tube it coule be the overflow. It isn't uncommon for a carb to have a float stick. Tapping it with the handle of a screwdriver can free it up.

Also if leaking from a tube, they have drain valves and it could be slightly open.

If from a gasket you should be able to buy a rebuild kit or have a shop fix it if your uncomfortable. ZipTye Racing is known for working wonders with those carbs if it hasn't already been modified.

Good luck.



  • Yz400f Jeff

Posted July 17, 2014 - 08:28 AM

#4

Could be alot of places it's leaking fuel from you won't know till you have a closer look could be bowl seal could be your a/p who knows, as to cleaning it out hold it wide open hold the decomposition in and kick it 5 or 6 times to clear out a flooded engine

  • kx4life13

Posted July 17, 2014 - 08:25 PM

#5

I recently got a yz 400 too, and my advice rebuild the whole carb do research on how to jet for where you ride the most because it is super touchy and do all that in one attempt cuz I'm going on three or four in a the month and a half I've owned it Haha. And starting I would mix a little of everything you read cuz these bikes aren't all the same with starting so try everything and when I clear out I pull in the decomp kick it three times then give it a quick twist (the accelerator pump makes holding it open flood the bike super quick) then do the kick ritual that works for your bike. Oh and my bike will start first kick every time!..... After I kick it 20 times to cold start it haha so it was probably warm or at least ran that day when the old owner showed you how "easy" it is to start but the bike is totally worth the pain in the ass first start cuz it feels amazing to ride and it does start first kick when warm

  • Yz400f Jeff

Posted July 18, 2014 - 06:24 AM

#6

Holding it wide open won't flood it, twisting the throttle multiple times will, the a/p only squirts a tiny bit with each twist, holding it wide open let's it get a hell of alot more air flow to clear it out, I never have to anyways because I know what not to do to so it doesn't get flooded I never touch the throttle before starting each bike is different though

  • kx4life13

Posted July 18, 2014 - 08:50 AM

#7

The person I bought mine from said to clear it out before starting it and either way it's still useless to hold the throttle open while starting plus having it open makes it kick back
And I said twist it once not multiple times

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  • Yz400f Jeff

Posted July 18, 2014 - 12:11 PM

#8

I'm saying hold it wide open hold the decompression release in and kick afew times to clear it out when need be.

  • Yz400f Jeff

Posted July 18, 2014 - 12:13 PM

#9

Should never give throttle when trying to fire it up I'm aware.

  • kx4life13

Posted July 19, 2014 - 10:27 PM

#10

I figured you knew cuz well if you do it more than once you either don't have feeling in your leg or your just a slow learner haha mine pretty much throws me off when it kicks back. I was more clarifying for the person we are helping haha so they didn't kick it with throttle wide open

  • Bethlehem

Posted July 20, 2014 - 02:09 PM

#11

 I got pictures of where the leak is. It's leaking from the hose that the arrow is pointing to, and also seems to be coming from the seam the other arrow is poingting to. - Now that I know how to start it, it actually runs like a dream. But the gas is leaking really bad. I don't know enough about this carb to rebuild it myself but I thought if you guys know what would cause a leak from this area I might be able to handle a gasket or float replacement myself.

 

IMG_0282_zps003d3dcc.jpg



  • grayracer513

Posted July 20, 2014 - 03:20 PM

#12

The hose is the overflow tube, and it leaks there because it's flooding.  It's flooding because the float needle is worn out, or damaged, or just dirty, or because the float doesn't swing freely on its pivot, or it's not assembled or adjusted correctly. 

 

As to the other leak, that could simply be the gasket there, but could also be a ruptured accelerator pump diaphragm.



  • Bethlehem

Posted July 20, 2014 - 03:29 PM

#13

 

The hose is the overflow tube, and it leaks there because it's flooding.  It's flooding because the float needle is worn out, or damaged, or just dirty, or because the float doesn't swing freely on its pivot, or it's not assembled or adjusted correctly. 

 

As to the other leak, that could simply be the gasket there, but could also be a ruptured accelerator pump diaphragm.

 

 

 Thank you! Is the float accessible from the bottom of the carb? If I can get to it without having to mess with too much else I think I can handle a new float, valve and gasket. I have no idea how to mess with an accelerator pump.



  • grayracer513

Posted July 20, 2014 - 04:07 PM

#14

Yes, and so is the AP diaphragm.  That's the small cover with 3 screws.



  • kx4life13

Posted July 20, 2014 - 09:22 PM

#15

My bike leaked from the same spot and it was the float chamber gasket





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