Ask 10 different people and you'll get 10 different answers on breaking in... I dont know about the STS motors but 2 liters of fuel before leaning out sounds like waaaaaay too much. Perhaps you were running it in too rich, which puts even more stress on the conrod as it stretches. It is crucial to build the right amount of heat in the engine during break-in. Keeping it too cool only breaks the motor in for that cool temperature range. When the motor actually gets hot (racing temp.) The motor will re-seat. Now you have broken in the motor twice and will have a shorter life span if you plan on using it while at a racing temperature. As long as you run a overly rich setting nothing happens except the conrod wears out. When the engine is too rich there is so much oil going through the engine nothing can wear. If nothing wears how can the engine break in? You'll know when to start leaning when you remove the plug and feel if there is not a noticable parts bind or "pinch" at TDC anymore. I have never let the engine 4-stroke under load, only on the idleing 1st few tanks while flushing it out.
-This is just my .02
Keith