WR400F Decompression valve not springing back

2 replies to this topic
  • lemke88

Posted April 02, 2014 - 01:28 PM


I replaced the crank in my WR400F. After putting everything back together, I fired her up on the first kick! Awesome, right?

Well there is a slight oddity that I noticed, that I'm pretty sure was not there before. When cycling the engine with the kickstarter, on what I think is the exausht stroke, the decomp lever will go limp and I can reach down to the decomp valve and twist it back and forth with ease. The decomp valve and lever do not spring back to their original positions. If I cycle the engine past TDC, the levee and valve snap back into place and there is once agian resistance on the lever, and the decomp valve will snap back if I manually twist it with my hand. Also, when the engine is running, if I put my finger on the decomp valve, I can feel it slightly moving back and forth with the idle of the engine.


Everything seems to be running great, but I'm concered with this one issue. I'd hate to have a day in the dirt ruined because of a dumb issue.


Did I screw something up? Or is this normal and I've never noticed it before?


Please let me know if you have any additional questions.



Edited by lemke88, April 02, 2014 - 01:49 PM.

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  • Krannie McKranface

Posted April 02, 2014 - 03:22 PM


That is because there is a pin pressing on the decomp linkage inside the cam, to make the decomp work at low rpms (start up)

  • lemke88

Posted April 02, 2014 - 07:07 PM


That is because there is a pin pressing on the decomp linkage inside the cam, to make the decomp work at low rpms (start up)


Are you talking about the decomp linkage in an auto decomp cam? The 400s do not have an auto decomp cam. It's a valve that is on the front right side of the cylinder head, to the side of one of the exhaust valve buckets. It's connected to a cable that runs up to a small lever that sits under the clutch lever. When the lever is pulled, it rotates a pin, pressing down on the valve. 


See here: http://www.southbayr...achments/18675/


Now my first thought was that if this is in fact happening on the exhaust stroke, then the cam would be depressing the valve bucket, which would cause the slack in the decamp valve because there was nothing for it to press against. The problem is I have no recollection of this happening before the engine tear down. Now that I think about it, maybe I did not connect the spring correctly on the decamp valve assembly. I will have to check tomorrow. I very well may have solved my own question. Sometimes it's helpful to write it out.

Edited by lemke88, April 02, 2014 - 07:10 PM.


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