Well, I just burned a hole in the piston of my Hyper50. I'd been having trouble with getting it to run right since my crash a couple weeks ago. I replaced the glow yesturday to no avail, and I took the carb apart last night. I did find something interesting: the fuel line in the tank seemed to be sheading like a snake loosing its skin. I'm sure this was causing some of my previous problems clogging one of the fuel lines, but its pretty much clear so I couldn't really see it. I cleaned the whole fuel system and replaced the fuel line.
It seemed to run fine this morning but it sounded lean; smoke was good and temp was good. I kept adjusting it richer but the adjustments made no difference. I was getting near the end of my second tank and noticed the power down and then the motor starting getting worse. I noticed the glow plug wire was hanging off (this happens when the head gets hot enough to melt the soldier and the wire falls off the connector, but I didn't rationalize it at the time), so I brought the heli to a low level hover to examine the problem, then "POP", and that's all she wrote.
The glow plug look bad but still worked. It was very loose, and upon further examination the head screws were not too tight either. THe problem was probably the loose glow plug.
The moral of the story is that you should check the tightness of the glow plug regually, especially after a change, and check the head screws periadically as well.