Yep, jumper cables won't do it. Not because the cables are not up to the task, but because you are trying to pull all that current thru the little sheetmetal teeth tips on the alligator clamps. I bet you were arc welding at those points:). You need a hard bolted terminal lug or terminal battery connection with large surface area to transfer any ammount of current. When I spin mine I hold the compression release and spin it up to full RPM before I drop the compression release. This saves wear on the starter as the stored momentum of the flywheel helps it pull thru.
A couple of failed starts could indeed have it nearly hydraulicilly locked with excess fuel in the cylinder and there may even be some remnants of shipping/storage lube oil in the cylinder. Next time you try, leave the fuel off, and spin it a little bit with the compression release open to try andd clear the cylinder before you try and start it...
After you get it running and broke in, you will probably be able to hand start it, but not very easilly when cold... Mine is pretty tough when cold, but not so bad when at a reasonable temperature...
Also wear hearing protection, that thing will sound like a barrel half full of hammers rolling down a hill when running:)