motors overheating

Okay, so this isn't my first build, but it's a scratch build - an Elev-8 built up from spare parts lying around - I call it my Frankenstein quad: The frame measures around 28" or 711 mm. and AUW is around 1.4 Kg. The motors are Tarot 4006 620 Kv with 13"5.5 pitch carbon props. I'm using a...