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Judging by the hood, it's a cross ram. My vote, Too fat!
Excess fuel gets in the exhaust, A.I.R. does its job, wham...backfire! M.O.O. and $0.02
Tim
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SOME WORDS OF WISDOM HERE!from the previous post.
Your car is backfiring from where?
Intake? or Exhaust?You didnt specify,but i know by experience that your talking about backfiring out your exhaust.When your throttle plate is closed under your extreme high vac conditions as you described.Your engine is backfiring from either experiencing a very rich air/fuel condition or an exhaust leak,bad diverter valve.During this period of deceleration,are you experiencing plumes of black smoke from your tailpipes?(RICH)
Generaly speaking:
"Backfire" is popping through the carb.....usually due to a lean condition caused by improper air/fuel ratio and or timing.
"Afterburn" or backfiring through the exhaust is caused by an excessively rick air/fuel ratio and or timing.