1989 Acura Integra starting

My car sometimes starts and sometimes not, battery is fine, alternator is fine, but sometimes the car "will" start and sometimes "not", when it does the starter sounds and operates just fine, but when not starting, the starter wont even engage or click over, it as if theres no juice gettin to it, tried jumping across the terminals and there was barely a spark, even with a fully charged battery, you folks have any ideas? I'm fresh out!