Went out to move the truck over so I could get my wife's car in the garage and he backfired thru the carb and that was it. He will crank fine but wont "bust off". 454,Rv cam, 670 holley, Moroso HEI disti.. First time to have a backfire. 2000 miles on the engine. Gets driven weekly for the past 16 months. The last time I drove him was last Sat.. No probs.. Going out of town to check on my mom and have not had a chance to check for fire to the plugs. Have to get my wife out to hold the wire! Could it be the power valve? If the backfire caused that what would cause the backfire. Jump timing?