I think the replies above including mine were to state that a lawnmower engine could be started without a blade, but anything above 1500rpm will do some serious damage as in your case. Most newer lawnmowers will go right to a certain rpm as there is no throttle control and that would be bad if no blade is on, most gokart engine will rev freely with no load until the centrifugal clutch kicks in and that's usually around 1500-2000rpm, even when i used my 440cc snowmobile on the microsprint we ran there was only a centrifugal clutch on the end of the crank so there was no load until 3500 rpm, now when you lose a chain at high rpm there is usually some damage done.

You could probably start a glow engine with no prop but as the first question was related to tuning there is no way to tune a glow engine without load.

Think about the guys with boats, you can't tell me a boat prop is a very big load on a glow engine ( out of water ), but i also don't see them running wide open on the bench to tune their engines.