This is not "MY" break-in program. But it is basically what I believe. What I do is rooted in Motoman's Break-in procedure. He's a smart guy and his procedure, adapted to a kart engine, works for me.
The theory is that with the hard chrome faced rings, tight piston to wall clearances, and fine crosshatch found in cylinders today, you have a very short time to get the rings to seat right before the peaks of the cross hatch become worn too much to finish the job right.
I use 16 oz of 30wt non detergent oil (Shell ND 30wt)and I cover up the vents in the pull starter cage to build heat. Remember, we don't have oil filters, so we have to change oil often to remove the debris from the oil.
I break mine in on the dyno with several long, wide open throttle, hard runs after I get the engine up to temp.