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Backfire

Old Dec 21, 2008 | 08:27 PM
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TexasRho83
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Backfire

So I've noticed that my ol' girl will backfire sometimes when she's cold and I accelerate. She never does it when she's been running at operating temp for a bit, but yeah she's done it 2 or 3 times so far. I wanna say it's through the carb but I could be wrong...

Pondering on what to do about this situation.
 
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Old Dec 21, 2008 | 08:47 PM
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This has a 460 right, so I assume a 4 barrel? What carburetor are you running?
 
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Old Dec 21, 2008 | 08:51 PM
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Yessir, 460. I haven't checked the carb for model numbers but I'm thinking it's a Holley 750 4bbl
 
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Old Dec 21, 2008 | 08:57 PM
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In most cases, a backfire is caused by combustion happening at the wrong time (when a valve is open). This can be caused by a lean condition or improper timing. Check that the choke is closed while the motor is warming up, and check for any vacuum leaks as they will be more problematic when the motor is cold and needs to run rich. Check your timing, and by this point if everything looks okay you need to run a compression test.
 
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Old Dec 21, 2008 | 09:06 PM
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Originally Posted by fmc400
In most cases, a backfire is caused by combustion happening at the wrong time (when a valve is open). This can be caused by a lean condition or improper timing. Check that the choke is closed while the motor is warming up, and check for any vacuum leaks as they will be more problematic when the motor is cold and needs to run rich. Check your timing, and by this point if everything looks okay you need to run a compression test.
I found out my choke hasn't been closing and since it's electric I'm gonna put a test light on her to see if I'm getting juice out of the plug they pigtailed the wire to. Today was pretty cold and I started her up to keep her running but she was coooold and was having a hard time getting going. I usually can pump the pedal a couple times and she'll catch then feather the gas til she can walk on her own. Today was a different story. I pulled the air filter housing and noticed my butterfly lid was still open. Clamped it shut by hand and voila...she fired up on the first try. Pretty sure the vacuum leaks are non-existent. Timing seems good but will slap a light on it ASAP to check.

Thanks for the help, bud.
 
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