I have rebuilt engines that were run without filters (on full size vehicles) and some of the scratches in the cylinder walls were deep enough to get a fingernail into, and that is just rediculous. I hope you didn't think I was refuting your advice, you are correct that it is not good at all to run without an air cleaner, although contrary to your, and my own advice it is done on occasion for short peroids of time when trying to diagnose engine problems.

thanks,
George