This one is easy.

Advance the throttle using the transmitter trim control. Some big blocks are funky like this. When warm/hot, sometimes you need to advance it as much as 20-40% or more to get it to fire. It won't run away on you. But to be safe, the first time, try placing the vehicle so it can't run away. You'll get used to it. It will fire, the revs will build slowly and then you just trim it back to its normal idle setting. You'll be surprised how far you will need to advance the throttle trim.