440 wont start when hot.

Well I have been trying to tune my freshly rebuilt 440 and for some reason I cant get it to fire when I shut it off once I have it up to temperature. It will crank all day long just wont fire. What are some things that could cause this.

Another problem I have been having is that my engine will rev up just fine in neutral but as soon as I try to drive the car it is very weak and wants to die. What could cause this?

I'm hoping these are both tuning problems. I dont have much experience with tuning carbs/figuring out timing but I'd like to learn rather than give up and pay someone else to do it. Any suggestions?