Check simple stuff first, but please be more descriptive with your problem. So if I am reading you right, before you changed the fuel line it would run for a short time and then die and it's still doing the same now (after you've changed the fuel line)? You said no spark. Do you mean no combustion or you put a timing light or in-line plug tester on each of the plugs and observed no spark? If you've verified that you are getting a spark to each plug, is fuel feeding to the engine unrestricted. Is the fuel clean? Do you have a fuel filter, if so is the filter element clean? Is the fuel pump diaphragm intact? Have you messed with/rebuilt the carbs recently (float height adjustment off?). Did you remove/disconnect any wiring/harnesses in order to make room to change the fuel line (may not have reconnected wiring)? Just a few things to think about. Give some more details if you can.