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#1
06-16-2013, 08:39 PM
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exhaust backfire causes 72 firebird 400
started getting exhaust backfire's recently, very loud pops. does it on intial start up when cold and does not do it once engine is warmed up.Changed normal gas station last 2 tanks. running quadrajet. could it be vac leak, what else can i look for before i blow my mufflers apart thks.
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1972 Formula ram air, 406, 60916 cam, forged pistons,rods. stock 69 intake, 13 heads home ported, quadrajet, tri y headers, 3 in exhaust, 3.23 gears, auto, CE frame connectors 275/60/15 back 255/60/15 front. |
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#2
06-16-2013, 08:59 PM
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Intermittent pop in the exhaust usually means a failing condenser, assuming you don't have HEI. If you do have an HEI, it could be a module problem.
The problem is an indication of an electrical problem where it loses fire momentarily.
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Rich The real democratic American idea is, not that every man shall be on a level with every other man, but that every man shall have liberty to be what God made him, without hindrance. Henry Ward Beecher "The problem with socialism is that you eventually run out of other people's money." Margaret Thatcher |
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#3
06-16-2013, 09:09 PM
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running pertronix in original dist
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1972 Formula ram air, 406, 60916 cam, forged pistons,rods. stock 69 intake, 13 heads home ported, quadrajet, tri y headers, 3 in exhaust, 3.23 gears, auto, CE frame connectors 275/60/15 back 255/60/15 front. |
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#4
06-16-2013, 09:49 PM
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Too rich at idle or mild flooding at start-up [?]. Leading to excess fuel getting in exhaust and igniting. How do the plugs look ?
Jim
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65 Catalina sedan. Allen Thomas Performance 495. KRE Heads at 310cfm ported by SD Performance, ProSystems Dominator carb on ported Victor intake, P-Dude custom grind hydraulic roller, MSD ignition, 3.50 Moser/Ford rear. F-Glass front bumper by son Rob, rear by the old man and joint effort for trunk lid. 3950# w/driver. Best of 9.5761/139 on 175 shot, 6.01 /114 in 1/8. |
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#5
06-17-2013, 07:27 AM
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The exh system on a cold motor that was just started up does not have enough heat to light off extra un-burned fuel!
I would pull the Q-jet apart and I bet you will find that the primary power piston it somewhat hung up and not providing enough enrichment, or you have a vacumm leak some where. Is the motor hard to re-start when fully hot, as in cranking slow?
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Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs! And he was not talking about 1/8 or 1/4 mile ETs! 1) 1940s 100% silver 4 cup tea server set. Two dry rotted 14 x 10 Micky Thompson slicks. 1) un-mailed in gift coupon from a 1972 box of corn flakes. Two pairs of brown leather flip flops, never seen more then 2 mph. Education is what your left with once you forget things! |
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#6
06-17-2013, 01:32 PM
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Do you have to pat the gas a lot to get it to start cold? If you fill the exhaust with unburned vapor and then throw an exhaust flame into that, it'll bang pretty good. Also verify base timing hasn't slipped and become retarded.
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I could explain all this to the girl at the parts store, but she'd probably call the asylum. White '67 LeMans 407/TH350/Ford 3.89... RIP Red '67 LeMans. 407/TH400/Ford 3.25 |
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#7
06-18-2013, 08:39 AM
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car starts just fine when hot and cold needs a few pumps of the gas but same as its always been, have not had a lot of time to track things down but so far i found the dist advance bushing had fell out-using piece rubber hose-but that should not be the problem and of course i pull my timing light out and it does not work so i need to pick up another one to verify timing.
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1972 Formula ram air, 406, 60916 cam, forged pistons,rods. stock 69 intake, 13 heads home ported, quadrajet, tri y headers, 3 in exhaust, 3.23 gears, auto, CE frame connectors 275/60/15 back 255/60/15 front. |
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#8
06-19-2013, 12:42 PM
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went and got a new timing light hooked it up and guess what #1 cyl is firing intermittently, put new plug in and looks good now, hope this was my problem
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1972 Formula ram air, 406, 60916 cam, forged pistons,rods. stock 69 intake, 13 heads home ported, quadrajet, tri y headers, 3 in exhaust, 3.23 gears, auto, CE frame connectors 275/60/15 back 255/60/15 front. |
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#9
06-20-2013, 07:20 AM
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That should do it unless it was a bad cap or plug wire .
__________________
Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs! And he was not talking about 1/8 or 1/4 mile ETs! 1) 1940s 100% silver 4 cup tea server set. Two dry rotted 14 x 10 Micky Thompson slicks. 1) un-mailed in gift coupon from a 1972 box of corn flakes. Two pairs of brown leather flip flops, never seen more then 2 mph. Education is what your left with once you forget things! |
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