1974 GMC C1500 POPPING AT MID THROTTLE ONLY

1974 GMC C1500
13,000 MILES • V8 • 2WD • AUTOMATIC
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NUTEDOGG
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1974 350 CHEVY ENGINE IN A 92 S-10BLAZER. ENGINE RAN FINE UNTIL I ADDED FUEL AND CHANGED THE PLUGS IN IT. SINCE I HAVE TRYED CHANGING PLUGS AGAIN, NEW PLUG WIRES, CARB REBUILD, TIMING ECT. IT RUNS FINE WIDE OPEN, AND AT IDLE. ONLY AT BUSTS UP AT PART THROTTLE WITH A LOAD ON IT. PLEASE HELP.
Sep 22, 2009 at 1:21 PM
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DOCFIXIT
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Take a fuel sample let it sit see if water is in fuel. Got points or HEI? carb 4bbl Quadrajet?
Sep 22, 2009 at 1:48 PM
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NUTEDOGG
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YES SIR, ITS A ACCEL H.E.I. DISTRIBUTOR AND IT HAS A FRESHLY BUILT EDELBROCH 500 CFM 4 BARREL CARB. I COMPLETLEY DRAINED THE TANK TODAY AND FLUSHED THE LINES WITH GOOD 93 OCTANE FUEL. I PULLED OFF THE VALVE COVERS AND CHECKED THE ROCKERS, PUSHRODS, AND VALVES FROM THE TOP AND ALL LOOKS WELL. STILL POPPING THO.
Sep 23, 2009 at 6:17 AM
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DOCFIXIT
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Is there vacuum advance on Dist? If yes pull hose hook timing light run engine up see if timing advances 18-20 degs. if yes hook hose run up should advance 35-40 degs. Have you adjusted A/F ratio up to richen mix. Maybe having lean miss.Whenit breaks up does it backfire? out exhaust or intake?
Sep 24, 2009 at 12:03 PM
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NUTEDOGG
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THE TIMING IS WONDERFUL. WHEN IT POPS IT POPS THRU THE CARB, THEN THRU THE EXAUST. CARB IS FAIRLY RICH AS WELL. COULD IT BE THE DIST. SHAFT BUSHINGS WORN???
Sep 27, 2009 at 6:40 AM
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DOCFIXIT
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Did this poping just start or did it start after a change to engine? is there vacuum advance?
Sep 27, 2009 at 3:52 PM
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NUTEDOGG
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correct it only started after i changed the spak plugs originally. yes sir, it is vacume advanced.
Sep 30, 2009 at 12:37 PM
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DOCFIXIT
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O.K. AC delco plug R44T or equalivent used?
Firing order 1-8-4-4-6-5-7-2 check to see oif 5 & 7 got swaped
Timing 9.5 ATDC
Sep 30, 2009 at 12:52 PM