hi is ti true that when the air temperature is higher you need more compression and to lean the engine?

We generally don't mess with the compression but yes, the engine will have to be leaned slightly with higher temperatures. Colder air is denser so you have to richen the needle to keep the mixture the same.

It is a fact that any change in: temperature,atmospheric pressure and humidity affect the setting of any IC engine and more so with small glow engines. When your engine is set for maximum optimal performance it will be over a very narrow range and any change will offset that balance. It is only important for record setting trial, for regular racing having a reliable run take precedance over absolute power

Just ask Andy Brown ... who (vainly) tried to race the WC in Europe , with his USA tuned engines.