Chainsaw Repair

Hi, new member here hoping for some advice.  I have a Husky 51 which seems to have too much compression to turn over when I pull the starter rope.  It's never been an easy starter, usually requiring a lot of pulls (until warmed up).  But now, I can barely pull the rope. This model has no compression relief.  I've done some research on the web and here's what I've tried. 
1. Removed spark plug and it pulls freely. Added a few drops of Marvel Mystery oil.
2. Inspected starter assembly, no damage.
3. Removed bar and chain to verify that's not binding.
4. Removed muffler to inspect for clogged exhaust port.  With the spark plug removed, I can watch the piston moving freely, but with plug in place it still pulls too hard.
5. Removed carb to check for obstruction.  Same story as with the muffler: it pulls hard unless the plug is removed.

The last time I ran it, about 2 months ago, I was working on a large dead fallen poplar.  The chain was binding or clogging and the saw started to run hot. I stopped, with the intention of sharpening the chain and putting some support under the tree...but it was dinner time and I never got back to it until now. I'm at a loss as where to go from here (other than to the store for a new saw) While old, the saw hasn't seen all that much use, just the occasional tree in the yard.  All suggestions will be appreciated.

Thanks, Cut4fun.  After tearing it down, cleaning,  and reassembling, it's back to normal.  The good news is that all is well, bad news is that I still don't know why it happened.