Need help on figuring out what has just gone wrong on my 1971 Spider 1750 (Spica Injection). It was running fine a week ago but refuses to start today. When you turn the ignition key, you can hear the fuel pump, and the engine turns over normally on the starter motor. It then just refuses to catch and start up normally. Any suggestions ? It does feel like it is not getting any gas as the exhaust is clear. I did a visual check on the gas tank visually and it is half full.