I have a 1975 280z and as i was driving down the road it just cut off. At first i thought i might have just run out of gas. It still wouldn't start after i added a couple gallons. Once i got it back to my house I checked the spark and gas. It has plenty of both but it only backfires. So the engine turns over but it will not start and it has not started since it has died. Anyone have any idea of what it could be?