Nope, most likely your sleave is shot. Just order a new sleave/piston and you'll be fine. Also, if it's not starting when it's hot, it means you are experiencing vapour-lock. A condition in which the fuel that enters the carb boils off almost immediatly due to heat, reverse pressurizing the fuel line and forcing all of the fuel out of it and back into the tank. This makes it impossible to prime and therefore start your engine, and occurs because your carb and therefore your engine is overheating. You NEED to use a temp gauge if you are new to Nitros and don't know how to tune them, no exceptions. A lot of people here will tell you not to use one and to tune by sound, but all us newbies will say otherwise. While tuning by sound may be the best way, it implys that we have some fore knowledge of how a nitro is supposed to sound, and since it's our first, we unfortunatly don't. Just use an infared temp guage like the one from Duratrax and aim it straight at the glow plug from about 1" away (Straight/verticle being the oppurtune word). The minimum temp for an ABC, ABN, etc sleaved engine is 200F, anything lower will cause accelerated wear on the pinch in your sleave (ABC, ABN, etc sleaves are "tapored" near the top, this is because the piston and sleave are made of different metals and expand at different rates when heated. The "pinch" allows the piston and sleave to continue to make a good seal with each other at varying temperatures) and create precisly the same problems as you're experiencing (Constant overtemp despite tuning, loss of compression, loss of power, start to start, etc). The borderline temp is around 290F, and the absolute roof is 330F. I just know I'm going to get flamed for that but it's what I've been told by several sources. Whereas the enemy of a conventional engine is heat, the enemy of an ABC is cold. Heat does far less damage than cold, in fact all it can do is put extra strain on your piston and conrod, result in a gallon or two of reduced lifespan, certainly not as bad as running it cold and a cheap repair at that.

And about the ambient temperature... As air heats up, it's molecules spread out and become more sparse, meaning your engine will not be getting as much air, and will in fact run cooler and richer. As air cools down, the opposite occurs and the molcules pack together more tightly, allowing the engine to recieve more oxygen on intake, meaning your engine will run hotter and leaner. The last thing you want to do is use your hi-speed needle as a thermostat thinking you need to keep heat in your engine, this is a mistake a lot of newbies make.

Hope that helps!