1974 Nova Backfire HELP!!

CrateCamaro · 06-22-2012, 01:14 PM

Im working on a 1974 Nova with the following engine:

350/041 heads/292H Comp Cap/HEI Ignition/Air Gap intake/650 Holley/Headers/Magnaflow Exaust

Car has backfired probably about 200 times in the last 10 years. Sometimes it runs good, other times it runs like a bag. Very Lazy.

Came to my shop a week ago, changed the power valve and it hasnt run since. I dont think its ever run good so thats why im in search of an answer. Changed the carb first with a good 750 and it will sit and run ok but as soon as you rev it, it pops and sprays fuel out the carb and then a 4 foot backfire. Pulled the intake checked all the lifters...very good...checked the pushrods, re sealed up the intake with new gaskets and set the rockers at 1/2 turn preload. Same backfire. Reset the rockers at .008,( thinking the lifters were pumped up) same back fire. Checked the timing numerous times. 34-36 degrees total.
Changed the distributer with two other good running HEI units...same backfire. Changed the plugs, wires, cap, rotor, mod,coil, wiring inside the distrib, hotwired the HEI right to the battery....same backfire. Changed the fuel pump...new line from the carb to the pump. Same. Car only has one vacuume line from the booster to the back of the carb....changed that as well with no luck. Just pulled the front of the engine down to see of the cam timing was off....its perfectly lined up. Chain is a bit loose but not enough to cause this problem. Compression test was ok...150-160 across the board and a leakdown shows no more than 10% on a stone cold engine.
This thing is fouling the plugs like crazy too.

Im reaching out for help here boys....ive been poped in the ear about 60 times in the last week and I cant take it anymore. Please help!!

06-22-2012, 01:14 PM	#1
CrateCamaro Member Join Date: Nov 2007 Location: Ontario Canada Posts: 411 Likes: 1 Liked 19 Times in 7 Posts	1974 Nova Backfire HELP!! Im working on a 1974 Nova with the following engine: 350/041 heads/292H Comp Cap/HEI Ignition/Air Gap intake/650 Holley/Headers/Magnaflow Exaust Car has backfired probably about 200 times in the last 10 years. Sometimes it runs good, other times it runs like a bag. Very Lazy. Came to my shop a week ago, changed the power valve and it hasnt run since. I dont think its ever run good so thats why im in search of an answer. Changed the carb first with a good 750 and it will sit and run ok but as soon as you rev it, it pops and sprays fuel out the carb and then a 4 foot backfire. Pulled the intake checked all the lifters...very good...checked the pushrods, re sealed up the intake with new gaskets and set the rockers at 1/2 turn preload. Same backfire. Reset the rockers at .008,( thinking the lifters were pumped up) same back fire. Checked the timing numerous times. 34-36 degrees total. Changed the distributer with two other good running HEI units...same backfire. Changed the plugs, wires, cap, rotor, mod,coil, wiring inside the distrib, hotwired the HEI right to the battery....same backfire. Changed the fuel pump...new line from the carb to the pump. Same. Car only has one vacuume line from the booster to the back of the carb....changed that as well with no luck. Just pulled the front of the engine down to see of the cam timing was off....its perfectly lined up. Chain is a bit loose but not enough to cause this problem. Compression test was ok...150-160 across the board and a leakdown shows no more than 10% on a stone cold engine. This thing is fouling the plugs like crazy too. Im reaching out for help here boys....ive been poped in the ear about 60 times in the last week and I cant take it anymore. Please help!! __________________ Tony Valerio 1968 Camaro 1700 IHRA H/CM 1701 NHRA SS/?A Last edited by CrateCamaro; 06-22-2012 at 01:17 PM.