Stihl MS291 Strange Problem

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"I've run into a Stihl MS291 "...hints it's some one else's saw. It may mean you have never heard it running ...or recently so.
That paints a different picture from your owning it but I find that confused by another statement I find peculiar....

"the engine has had remarkable power to the point where a decomp valve would have made a nice addition"...I got the impression that your compression varies....if so then you have a ring/piston/bore/head issue....compressions go down with significant use...not up ...well, unless the head is choked up with carbon...Do you know this apparently varying compression from experience with the saw? or is that something you have been told.

Mentioned was checking flywheel clearance and coil tightness...good thinking..Watch the flywheel with cover off and turn by hand...any side-to-side at all? "Whap whap' could even be a seal passing oil/air. It could be in the exhaust...I'd check that. I'd then see what happens with the noise when muffler is 'off'.

If the noise is absent with plug-out...can you hear it when compression tester screwed-in?..

I think the rest has been covered...
 

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