Hello fellas

I decided to run my 09 on the bench today to clean up the dust and the strangest thing happened: it wouldn't start!
I spent half an hour flipping the prop to no avail. I disconnected the fuel line to remove excess fuel, but still no pop. I even gave it a whif of the electric starter (lots of fuel coming out the silencer), but still no signs of life, the same happening with pure ether shots. I then removed the silencer and within 8 flips is started to pop, finalling starting after 2 dozen flips or so. With the engine warmed up and set, compression and needle wise, I removed the head and put the silencer back on. No pop, no nothing once again. Removed it and presto, a few more flips and it started running (pretty well actually, peaked 10200 with a aviomodelli fiber 9x4 prop).
Oh, thottle response seemed a little sluggish from WOT to 5000 rpm.

I simply don't get this, I have had it running from new with the muffler, somewhat easy starter and sipping virtually the same old english mix (though I cut the oil a bit down today from the usual 30% to something like 23~25%), freshly made. What could have happened or what can be causing this?

Thank you