Did you pull the little brass jet out and clean it or just leave it in there, I have found sometimes crud can get stuck under the jet.
Also if you choke the motor while pulling the rope will it attempt to start? Its been an old trick I use if its a minor blockage the extra suction will generally remove a partial blockage. Also I found a lot of these engines really like a snorkel attached, without they can be a bit piggy.
