Snow, what year is your YJ and what engine is in it? I've got a '90 with the 4.2 and had the same issue a few months back. I ended up replacing the pump, filter and carb along with installing new rubber fuel lines from the pump to the carb with no luck. In the end I replaced the gas cap and it started right up. Make sure your getting good spark then pull the gas cap and try starting it. If that works, replace the gas cap. Also, make sure your evap system is functioning correctly. You could have a restriction somewhere in it as well causing fuel delivery issues. One last thing regarding the fuel pump. If it's mechanical, did you make sure the pump armature was properly seated on the cam lobe?