Re: Backfire... What to do?
[Re: Whitey Nocar]
#1895721
08/20/15 01:24 AM
08/20/15 01:24 AM
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Joined: Oct 2006
Posts: 1,264
New York, USA
Chargerfan68
pro stock
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pro stock
Joined: Oct 2006
Posts: 1,264
New York, USA
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I had exactly the same problem with my 73 charger...stock 440 recently rebuilt. I tuned the carb with a wideband and it started doing that. I was close to 14.5 at cruise and when I would let off the gas at about 65, boom a few times at the mufflers. They are pretty expanded now after a bucnch of backfires.
I tried a whole bunch of things, but what cured it was me going up 2 jets and slightly raising the float level.(I had it slightly on the low side). Now my cruise is in the 13s, but no more backfires at all.
Just my experience, but it is easy for you to try as a test.
Good luck.
1.50 60Ft. , 10.75@ 127MPH Hauling 3900 LBS.
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Re: Backfire... What to do?
[Re: Whitey Nocar]
#1895790
08/20/15 09:43 AM
08/20/15 09:43 AM
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Joined: Feb 2005
Posts: 28,312
Cincinnati, Ohio
Challenger 1
Too Many Posts
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Too Many Posts
Joined: Feb 2005
Posts: 28,312
Cincinnati, Ohio
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So my ride likes to backfire on the highway, usually only once, but maybe that's because once it happens I try not to drive in a way that will make it happen again.
Let me explain... I get up to speed. 70-75mph and the car wants more so I excellerate. When I let off the gas it's like the exhaust fills up with fuel and kaboom! Not sure if it's a fuel mixture thing or possibly a exhaust gasket leak that somehow sucks in oxygen and the mixture is just right that the heat makes it blow. I'm obviously not a mechanic, that's why I'm looking for advise. My guess is exhaust sucking in on the deceleration because nothing has changed on the carb as far as I know and this seems to be a somewhat new phenomenon.
Any ideas?
Btw the car is '68 coronet with 318, intake, headers, dual exhaust, carb.... Everything else stock and never rebuilt as far as I know.
PS. Small to moderate leak in gas tank when filled more than 1/2 a tank. Don't think that contributes to the problem, but the combination of the leak and the backfire is probably not ideal.
Does your car have power brakes? My 74 started back firing on decell, mine started coming down Pikes Peak mountain while in 1st gear coming down. Turned out to be my power brake booster was leaking vacuum. Replaced it and no more back fires. Just replaced a gas tank in one of my cars a couple weeks ago. Developed a crack in the top and caused it to leak when full. I replaced the tank, can't have it leaking. Good luck finding your vacuum leak...I doubt it's the exhaust personally.  
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BTW, are you trying to make the early evening news with that gas tank leak making a potential fire bomb 
Fix that rascal, gas leak, right away so we don't loose another classic Americn muscle car 
