1973 Chevrolet Monte Carlo backfire through exhaust

Tiny
MELNJEFF
  • MEMBER
  • 1973 CHEVROLET MONTE CARLO
  • 5.7L
  • V8
  • AUTOMATIC
  • 99,000 MILES
Put new motor in was told it was a stock 350 but had a bad head gasket. Pulled heads and found it to be punched 30 -40 over. Put new head gaskets in on both sides. Had points dist. Swapped it out for a HEI. Did everything by the book a friend adjusted the valves but they wont stay adjusted and start knocking. Changed plug wires and plugs it idles fine but in gear the higher the RPM the backfire starts popcorning out exhaust on left bank only and falls on its face but yesterday it started popping on both left and right banks after driving through puddle of water. It got louder and louder car died out a few times acted like it wasn't getting fuel wouldn't stay running hard to start loss of power and limped it home I'm stumped please help. I'm pretty good with motors but don't know everything and this is the first I've dealt with this problem motor has a Rochester 2bbl headers stock intake the heads are stock.
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Friday, December 18th, 2015 AT 8:05 AM

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Tiny
HMAC300
  • EXPERT
Pull the valve covers off and check to see how far valve springs are going down, it may have a bad camshaft in it where a lobe is worn down. Then check pushrods for being bent and worn on tips. If cam is bad replace cam and lifters and use something similar to stp or graphite grease on cam lobes and lifter bottoms. To check for bent pushrods roll across a flat surface like a table.
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Friday, December 18th, 2015 AT 9:34 AM

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