cannot start my yz400f

11 replies to this topic
  • heineken4menotu

Posted October 24, 2008 - 03:17 PM


I took apart the carburetur and was wondering what the settings for the black knob on the outside of the carb and the one up underneath the carb?:lol:

  • DeeCee

Posted October 24, 2008 - 05:58 PM


The black knob on the side adjust the idle speed so there is no specific setting as this has to be done when the engine is running.

The screw underneath adjusts the mixture. For a first start set it at 1 and half turns out from the fully in position.

While you have the carburettor apart make sure all the passages are thoroughly blown through with compressed air.

  • heineken4menotu

Posted October 24, 2008 - 06:25 PM


I tried that but still it still hasn't even fired. Does that black knob need to be adjusted to get it started because i have it all the way backed off.:lol:

  • tcmII

Posted October 24, 2008 - 06:30 PM


You will need to turn it in a little. The slide needs to be up a little to get some flow through the carb.

  • heineken4menotu

Posted October 24, 2008 - 06:37 PM


You will need to turn it in a little. The slide needs to be up a little to get some flow through the carb.

how much is a little?

  • heineken4menotu

Posted October 28, 2008 - 05:44 AM


i just took it to the shop and now they're saying that they can't figure it out either. I changed the plug, cleaned the carb, valves adjusted, new oil, new air filter, new fuel, and cannot figure it out.

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  • intensem1rider

Posted October 28, 2008 - 07:06 PM


Did it start before you adjusted the valves? Are you sure the timing is on 100%?

  • maverick_26

Posted October 30, 2008 - 08:52 PM


I've had a problem like this before when I had my yz400f. If you dont torque the cam caps down in sequence to the correct torque like the manual states it can actually freeze the cams, and make the cam sprockets turn on the camshafts when you go to kick it to start it. I was stumped for about a month, because everytime I would check timing on the sprockets it was right on. The intake cam sprocket had actually turned enough to where when the piston was at top dead center the lobe was pushing the valve partially into the cylinder, creating a no start condition. Keep in mind, when the engine is at TDC using the flywheel sight mark, take off the valvecover and check the cam lobes. They should be facing slightly up/outwards from eachother, neither of them touching the valve buckets. Hope this helps. :lol:

  • motojoe_23

Posted November 01, 2008 - 04:52 PM


Rotated cam is a very real possiblity.

Do you have the OEM exhaust? If not, Id say the mixture will be closer to 2 turns out.

Try turning the idle in most of the way as well. That way it should start if it is tuned right, and no other major issues, but will idle high. Then when it is warmed up, adjust the idle back down. Blip the throttle after every time you turn the idle knob, to re seat the throttle.

  • DeeCee

Posted November 02, 2008 - 07:40 AM


You haven't explained why you stripped the carb down in the first place.

How was the bike running before you did this ?

Please tell.

  • heineken4menotu

Posted November 06, 2008 - 08:29 AM


I got the bike running and it was great. There was a wire going to the cdi that was disconnected (maybe from vibration?):worthy: . Anyways now it gets hot quick, it seems like a never ending fixer upper. I'm just gonna sell it and go back to riding a two stroke, unless a find a 450 in my price range.:eek:

  • 1998YZ400F

Posted November 06, 2008 - 02:54 PM


but once you fix it up, they are beasts and extremely reliable bikes when taken care of. i have done lots of work on mine as well but it still runs fine

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