Cannot get my car to start after rebuilding engine

I rebuilt the engine and after I completed the rebuild the engine started up and ran. There was no noise coming from the engine. I took it for a drive around the block then the engine stopped working and would not restart. It sounds like it is not getting gas or spark. I checked the spark and there is spark coming from the spark plugs. There is gas smell from the cylinder and the spark plugs were wet from gas.
why would the engine run for a while then stop running?
any suggestions