Won't start new motor
Is it carved or efi??If efi do this::locate your throttle body,pull the air intake hose loose from the throttle body,spray starting fluid or carb cleaner into the throttle body opening, push the hose back onto the throttle body then try to start the car.If it starts & runs for a few seconds then dies,you've got a No Fuel problem.If it doesn't start at all,you've got a No Spark problem.If its a no fuel issue,turn the key on & listen for the fuel pump priming sound.If you don't hear it,check for a blown fuel pump fuse,defective fuel pump relay,a defective computer power relay or a tripped inertia switch.If they're OK,disconnect the harness at the fuel pump,turn the key on and use a voltmeter to test for battery voltage.If voltage is present,the pump is bad.If voltage isn't present,but its present at the fuel pump relay harness, there's most likely a short/open in the wiring harness between the FP relay & pump.You didn't list your vehicle info,so I'm unsure of which type ignition you've got.
Most no starts on a new engine are caused by a ground wire you forgot to connect,wiring harness not plugged in or a timing issue.