5_spot, if the line broke just from moving it, that would likely have been sucking in air for quite a while, it doesn't take much, that's for sure.

As for seizing, the Evo engines are ABC, so, actually, the piston-liner fit gets LOOSER as the engine heats up, because the liner expands faster than the piston. So, overheating won't hurt the piston-liner, it will just cause the engine to slow up and loose power, but won't hurt it or seize up. (However, in theory you could cause the conrod or other parts to seize, but if you do that, the result would be a broken engine, I'd think. I've seen broken rods, and other bits but never just from running hot. And I've overheated my share of engines). Also, believe it or not, some engines will run cooler with less oil, while others want more. 18-20% oil is pretty safe for most engines and most oil blends. Some oils work better than others, so you can use less, some engines need more oil than others. I wouldn't bother running a new Evo on anything higher than 20% oil, and 18% should be just fine.

Also, when an ABC engine over heats, it doesn't just quit all of a sudden. You get a drop in power and rough running for a couple of seconds, it takes a little time to get over temp. (I had a long battle with engine overheating on one of my planes a while back. finally fixed it with a helicopter-style heatsink head and some much bigger holes in the cowl. It was a "long" battle because I REALLY didn't want to cut up the cowl like I finally had to). Oh, and you usually have to really work at it to get a non-cowled engine to overheat. I'm talking seroiusly lean running.

Now, if you had a ringed engine, over heating and seizing up the piston is absolutely possible and very very bad, almost instant paperweight.

Btw, if you can track back a source of air bubbles to something besides fuel tubing, you can often seal things up with RTV silicon, available at autoparts stores (get the high temp stuff, obviously). I've used it around fuel tank stoppers, on fuel fittings, carbs (espeically where the carb mounts on the crankcase) and remote needle fittings etc. Works great. Oh, you can't "fix" fuel tubing, just replace it if there is any doubt. Tubing is cheap.

On final thing I forgot before, I've seen the Alpha's fuel tank split at the stopper a few times. Once it filled a guy's fuse full of fuel. Other times, it just caused the engine to run poorly. If you haven't already, pull the tank and inspect around the stopper. You can do a tank pressure test by putting it in a sink full of water, with the fuel lines out of the water of course (no water inside the tank please). Then plug one line and blow in the other, then pinch it off. Look for bubbles. If you see any, fix it until you don't anymore .