Problems with the first start of the day on my YZ 400, wierd?!?

4 replies to this topic
  • lump-dog

Posted January 15, 2001 - 03:14 AM


Lately, every time I unload my '98 yz400f and start it for the first time of the day, I have trouble finding TDC as I kick through the stroke. Gone is that familiar spot that I need my compression release to kick through before I bring the starter back up to the top and give 'er a kick. I find my self having to just kick randomly, because TDC is'nt discernable from the other little "hard" spots that are present. Sometimes, when I'm mindlessly kicking through the stroke the TDC "sweet spot" randomly reappears. This usually only happens on the first start of the day. The rest of the day everything seems fine, back to "normal". (By the way, just to clear things up, I've had this bike since it was new, I DO now how to start it, this isn't a "technique" issue). What's up, any ideas? At first I thought my compression release was hanging up, but on the outside, everything seems to be working ok. Just hoping there's a simple explanation and I don't have to tear in to the thing. Thanks in advance.

  • Matt406

Posted January 15, 2001 - 05:08 AM


It sounds like you have a compression problem. I can think of two things that might be happening. First, you don't have any compression because the piston and/or rings is worn out. You will need to replace these. The other problem may be the valves. If they are not adjusted for the correct clearance, one could hang open and be releasing the compression just like if you were holding th decompression lever down. Have you adjusted your valves lately?? If not, then adjust your valves and try again.


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  • Hick

Posted January 15, 2001 - 07:32 AM



If I turn the idle down on my 426 I experience the same sensation, try turning up your idle a half turn.

Other than that I agree with Matt406 on the valve clearance, it is conceivable for them to be so tight that air is getting by the exhaust valves, but by this time I’d expect performance to suffer noticeably.

Of course you may just need a set of rings. A bleed down test (after you check valve clearance) will tell you for sure.

  • Tim

Posted January 15, 2001 - 09:57 AM


Sounds to me you are so exited to get out and ride the beast, you forget to think.... :)

Sorry, you opened your self up for that one. I hope it is nothing big. Do you pull in the compression release and kick a few times to lube up the cylinder before running in the morning? And how about lubing the compression release cable? If the valve sticks open a little this would also cause loss of compression.

  • jimt_yz400

Posted January 15, 2001 - 02:36 PM


Your compression release cable might be hung
up on the frame somewhere. There is not alot
of slack in the cable so any movement of the
mount for the lever might cause the cable to
become tight. This happened on my '98 and everytime you went to turn right the thing stalled. I remounted the lever and made sure that the cable was not tight when I moved the
bars (while it was runnin) and now all is well.
Make sure that the lever on the cylinder is
being retracted by the spring. I had a spring that wasn't quite mounted correctly after adjusting the valve clearances that caused a
similar sympton

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