After warm-up no compression?

4 replies to this topic
  • BC3

Posted May 19, 2007 - 09:06 AM


2003 YZ450..I just had the head repaired by Engine Dynamics in Petaluma CA
for the cam bearing surface (intake cam) gauling. The engine had maybe
two hours on it and started on the first kick cold and pretty much the same warm...I went to my practice track last night and rode for two hours pretty hard....I fell on a freshly watered corner and couldn't start the engine....
I kicked and kicked even with the Hot Start lever pulled...It just didn't have any
noticeable compression stroke? When it did fire up it ran kinda rough but still idled and had good horse power.....:) Any ideas, I sure don't want to think the head is screwed up again:crazy:

  • grayracer513

Posted May 19, 2007 - 08:52 PM


The auto decompression system isn't at fault. It reduces compression by releasing the first half of the compression stroke. If it fails, you'd have full compression at cranking speeds, not none.

So, when you got the bike running, and then shut it down again later in a more normal fashion, did it still not have compression, or does it loose it each time it warms up?

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  • BC3

Posted May 19, 2007 - 09:07 PM


Tried it this morning first thing (cold) not the normal feel but it started right up....I'm going to tear it apart and see what's going on....
I'm kinda pissed because I thought I had all the bugs worked out...Guess not

  • grayracer513

Posted May 20, 2007 - 09:13 AM


What I was getting at was, if this was a transient condition, something that happened once and not again afterward, then you could be looking at carbon sticking a valve stem, or something like that. If it happens that the compression feels low after warm up every time, then it's a more "permanent" mechanical condition, possibly the exhaust valve clearance being too tight, etc.

  • BC3

Posted May 20, 2007 - 03:51 PM


It seems to be like this all the time since the other night.....I hardly ever use
the Hot -Start lever, but since this has been going on it won't start without it
after warmed up......First kick with it? I guess I should take it apart and check the clearances. That way I will feel better.....

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