I recently obtained a 1971 240z with the L6. Drove it for two weeks then it idled erratically, backfired then wouldnt fire at all. It will still rollover.The distributor is still turning but no fire. I've replaced the points and the coil with no luck. As far as i can tell, the only engine part thats not original is there is a gm alternator. Anyone have any idea what i should try or what i should replace next?