Your engine is going lean and overheating. That's what would make it quit a few minutes into the flight. The going lean can be caused by many things. First off, though, get rid of the Easy Fueler. It's making a restriction, and could also be leaking air. You'll also need to check for any cracks and holes or other air leaks in the fuel tubing. Vibration can cause air to get agitated into the fuel, which also leans the engine.

Your Bisson muffler may not be giving the fuel tank enough pressure, so you are getting leaning due to low fuel pressure. Restrict the exhaust outlets to see if you get some improvement, or try the stock muffler to see if that helps. Many after-market mufflers just don't generate enough pressure to enable the fuel to move fairly well.

You may also find that the engine will run better and cooler if you go with a smaller prop, such as a 13 x 8 or so. Run the engine close to 12,000 RPM when leaned to just rich of peak RPM, and you'll find it has better performance, though louder.