Engine help!

Ok, i have got a 91 xj that i just put a new motor into. Now, when i first got the motor installed and started it up it ran just fine. At the time i only put water in the radiator to make sure it was going to run alright. I just dumped the water out and filled it up with antifreeze and went to start it and now all it does is start and then shut off right away. The idle on it will also jump around a lot. I just put a new fuel filter on it and that didn't seem to help.

What would be making it not want to run now? I need to have this ready for this weekend cuz i am taking it on its maiden voyage. Any help would be greatly appreciated.

Thanks,
Ben