Yesterday I ran my new-to-me 120 Surpass (no pump) for the first time. It started up nicely and everything seemed OK on the ground. After flying it I noticed a lot of fuel on the cowling that seems to be coming from the needle valve. I remember reading somewhere this is a bad gasket or o-ring. Do I need to tear down the carb?

In the air, on the down side of a loop and afterwards, it sputters. Back on the ground I ran it full throttle and held it (carefully away from my toes!) nose down, and after 6 or 8 seconds, it quits. (It occurs to me this might not be such a giant issue, since who needs to run full throttle straight down. But I want to find out what the problem is.) What's going on here? Is it possible it's simply too rich? I tuned it with my tach for quite a while before flying it, and it's turning about 9000rpm with a 15x8 prop. Is the leaky needle valve causing this?

Also, how hot is too hot? It seemed hotter than I would have guessed, but I'm new to 4-strokes, so it also seemed noisier and had a lot more vibration than I would expect (I'm told by an old hand that the two latter features are normal). I'm going to buy an infra-red temp sensor, but what kind of temps should I be seeing on the outside of the engine? Can I add extra oil to my fuel to help cool it?