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Backfire in the exhaust when decelerating
#1
Since I have my Mustang I always get backfire in the exhaust when decelerating. I know it can be a timing problem but what else ? It did it when I had the 2 barrel carburetor (and at that time the car seemed properly tuned), now I have a Holley 4 barrel and it's the same. What do you suggest to check ?
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#2
If it's the same and no worse with the 4 barrel than the 2 barrel could be an intake valve hung open by carbon build up causing exhaust stroke detonation. Get some Sea Clean and pour into the carb as recommended. Make sure the car is NOT in the garage. May have to repeat it after you drive it a while depending on the build up. Cheapest try.

[Image: 2rr7aiv.png]

Just cruising along minding our own business when BAM!!! The LAWS show up.
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#3
It's banging and it's a bit worse with the 4 barrel I have to say.
My exhaust is really poor, I need to change it and I'm sure there are some tiny leaks that can cause this but not sure. I will try what you said, thanks.
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#4
Depending on the type of exhaust system your running. (let us know) could be a back pressure issue. I recall you've done a lot of work. But why don't yo post up again what you heve and that will help in solving the problem without guessing.

[Image: 2rr7aiv.png]

Just cruising along minding our own business when BAM!!! The LAWS show up.
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#5
You're right, here we are :

72 Mustang Grandé
351 Cleveland 2V with WEIAND X-Celerator 4V intake

Holley 600 CFM carb since a few days (we tried to tune it properly and seems a lot better now)
Exhaust is a "custom" one, done by the previous owner, but it's a mess really, this will be the next thing I'll change for sure. I think there are a few leaks here and there. I'd like to get new exhaust headers + Flowmasters etc. Still have the original headers at the moment.
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#6
If the 4 barrel made it worse, I'de still be looking at carbon build up on a valve since your supplying more fuel. New exhaust is still a great idea. Let that rascal breath!!

[Image: 2rr7aiv.png]

Just cruising along minding our own business when BAM!!! The LAWS show up.
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#7
markmel would the 4v intake mess with the 2v heads?


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#8
Absolutely, Do you still have 2v heads? The port surfaces don't match and create all kinds of air/fuel turbulance issues. The 2v heads have an intake port opening of 2.02 X1.65 where the 4v head and intake has an intake opening of 2.5 X 1.75 inches. So there is a damming effect of fuel and air going into the 2v head from the 4v intake.

[Image: 2rr7aiv.png]

Just cruising along minding our own business when BAM!!! The LAWS show up.
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#9
That sounds like the cause right there. 4V intake on a 2V head. Get yourself a edlebrock performer asap. Try to find one cheap or on ebay.

2011 Buick Regal
2010 Ford F150 Screw
2002 Triumph Trophy
1973 Dodge Challenger RT
1972 Mustang Grandé Coupe
1954 Ford F100
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#10
Better yet, Get a set of those 4v heads and have a ball!

[Image: 2rr7aiv.png]

Just cruising along minding our own business when BAM!!! The LAWS show up.
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