Like mentioned before take a break (you most likely did already...lol) but a friend w/some mech. experiance would be a great help. I always recommend a second set of eyes while trying to start the new combo, to check for obivous leaks and problems.
I would also check the firing order again (like mentioned before and having the fuel pressure 7 or less. (5-7.5 depending on carb.) (like mentioned before)
Did you check the carb. before installing it????
Set the mixtures screws???
Set the butterflies in the carb.????
Do you have a return style fuel sytem???..or dead head???
What type of carb. do you have?? and size??
Maybe I forgot, but did you say there were any noises or back- fire threw the carb. or exhust??
I don't want to sound like a pro or nothing when it comes to carbs becuse I am not, but these questions do help out when you answer them
And any addtional answers about fuel and ignition would be great as well.