14 gauge isn't the problem. 14 gauge can easily carry 20 amps. AT ONE TIME, possibly long ago in National Electric Code, it was legal to run 14 gauge for a 20 amps circuits that didn't have lighting attached. I have seen Furnace blowers and such, wired, inspected and cleared with 14 gauge and 20 amp breakers. If there had been a light on it it would have flickered, badly. A small voltage flicker will make the lights flicker like mad. My NEC knowledge is 20 years old so... I REALLY don't like the paint showing on the wires. I THINK I see a little bit of paint left on that toasted neutral, hard to say. Clean it up, like other said, use a quality receptacle. Maybe get an infrared thermometor. They are useful for all sorts of things including checking receptacles.