Yz400f questions,

3 replies to this topic
  • Buzzy613

Posted February 22, 2016 - 02:59 PM


Hi there, I've been working on this bike for a few days now and it'll have this terrible exhaust back fire hanging idle situation. I've looked at all the sticky FAQs ect, I cleaned the carb emensly, and I just checked the valve lash, the exhaust valves take the min clearance with ease and 2 of the 3 also take the minimum clearance with ease. The furthest one from the cam chain is tight, would this cause this issue? Also I took a pic of the cam but am unsure if it is auto decompression or not, I am fixing the header to silencer leak this week also just in case it is that but it seems like a valve issue

Attached Thumbnails

  • 1456181913913.jpg

  • 0bigsilver6

Posted February 22, 2016 - 07:59 PM


Yes that is an auto decomp exhaust cam. The timing looks ok from what I can tell from the odd angle of the picture, assuming the piston is at TDC. I'd fix the exhaust leak if you know there is one already and report back. Also, you need to figure out what the actual valve clearance is. "The minimum clearance with ease" check doesn't cut it.

Edited by 0BigBlue7, February 22, 2016 - 08:00 PM.

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  • Buzzy613

Posted February 23, 2016 - 02:33 AM


From cam chain to the header pipe on the intake the lash is 0.15mm - 0.13mm - and less then 0.13mm
I just checked this morning so it must have changed from having it running for 6 minutes yesterday. My bad for the miss reading

Edited by Buzzy613, February 23, 2016 - 03:11 AM.

  • Buzzy613

Posted February 23, 2016 - 02:45 AM


And it would back fire like a shot gun out of the exhaust like it was loaded up with fuel after I took the plug out, kicked all the previous fuel out of the cylinder, dried the plug off, and re installed the plug, not decell pops but loud bangs when trying to start it and once it was running, it would look and snarle with little throttle movement.

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