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Marshall V. Daut · 12-29-2024, 07:53 PM

I agree that the popping noise you describe when letting off the gas is probably an exhaust leak emanating from the juncture between the exhaust manifold and where the muffler's vertical pipe meet. Moreover, I suggest you look at how the muffler-to-manifold clamp is oriented. If the gap between the two clamps is facing directly into the carburetor's intake throat, escaping exhaust will be sucked into the carb with a resulting "pop" noise when decelerating and the back pressure inside the engine is at its highest. Loosen the two clamp nuts and rotate the clamp halves so that the gap between them is not facing directly at the carb. See if that solves your problem.
And while you're at it, fix the exhaust leak. Not only does it cause an irritating noise, it also sends out carbon monoxide. On a long drive this poisonous gas can enter the passenger compartment and cause illness. Unless you bellied up to the bar and purchased an Aires muffler with the correct pipe flange, you probably have one of the old Midas cheapie mufflers with the flange that is difficult to seat against the exhaust manifold's flange. You can improve sealing by hammering the muffler pipe flange 360 degrees around a spare exhaust manifold and then transfer the muffler back to the car. Also, I ALWAYS use the red muffler sealant sold by vendors when mating the muffler pipe to the exhaust manifold, smearing it equally around the flanges. I know Ford didn't do that at the factory, but we are obliged to use repo parts that may or may not fit as Ford parts did. Using the sealant for me is peace of mind.
Between reseating the muffler flange (or installing an Aires muffler), applying muffler sealant paste and re-orienting the muffler clamp, that should solve your problem. And don't forget to check #4 exhaust port for leaks. If your exhaust manifold is drooping in the back there (and many do!), you will hear a ticking sound as the exhaust escapes. It could also be the source of popping on cold days when the hot leaking exhaust exits the manifold when decelerating and hits the cold air. If you don't hear an exhaust tick, though, you might be ok.
Marshall

12-29-2024, 07:53 PM	#5
Marshall V. Daut Senior Member Join Date: Apr 2011 Location: Davenport, Iowa Posts: 2,626	Re: Backfiring I agree that the popping noise you describe when letting off the gas is probably an exhaust leak emanating from the juncture between the exhaust manifold and where the muffler's vertical pipe meet. Moreover, I suggest you look at how the muffler-to-manifold clamp is oriented. If the gap between the two clamps is facing directly into the carburetor's intake throat, escaping exhaust will be sucked into the carb with a resulting "pop" noise when decelerating and the back pressure inside the engine is at its highest. Loosen the two clamp nuts and rotate the clamp halves so that the gap between them is not facing directly at the carb. See if that solves your problem. And while you're at it, fix the exhaust leak. Not only does it cause an irritating noise, it also sends out carbon monoxide. On a long drive this poisonous gas can enter the passenger compartment and cause illness. Unless you bellied up to the bar and purchased an Aires muffler with the correct pipe flange, you probably have one of the old Midas cheapie mufflers with the flange that is difficult to seat against the exhaust manifold's flange. You can improve sealing by hammering the muffler pipe flange 360 degrees around a spare exhaust manifold and then transfer the muffler back to the car. Also, I ALWAYS use the red muffler sealant sold by vendors when mating the muffler pipe to the exhaust manifold, smearing it equally around the flanges. I know Ford didn't do that at the factory, but we are obliged to use repo parts that may or may not fit as Ford parts did. Using the sealant for me is peace of mind. Between reseating the muffler flange (or installing an Aires muffler), applying muffler sealant paste and re-orienting the muffler clamp, that should solve your problem. And don't forget to check #4 exhaust port for leaks. If your exhaust manifold is drooping in the back there (and many do!), you will hear a ticking sound as the exhaust escapes. It could also be the source of popping on cold days when the hot leaking exhaust exits the manifold when decelerating and hits the cold air. If you don't hear an exhaust tick, though, you might be ok. Marshall