You mentioned you recently replaced the needle. I have had a couple of these flood badly and the cord snaps back because to much fuel is in the cylinder. So in short check the mower is not flooded by turning the fuel off, opening the throttle and lastly removing the spark plug and pulling the rope 10 or so times.
Remember the needles need to match the primer cap. The aftermarket caps work better with the shorter needles. The genuine caps which I always use work better with the slightly longer needles.
In my experience when the decompressor's go faulty the engine wont start or its usually very difficult to start them because the decompressor doesnt seal.
All of the other suggestions above a more likely but I thought I'd add one more.
Big Ted might have some other suggestions - just wait for him to confirm as well.
