1975 corvette backfiring
Thread Starter
Cruising
Joined: Oct 2023
Posts: 12
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From: New york
1975 corvette backfiring
My car idles good, but as soon I give it gas it backfires through the carb. I checked the timing meticulously at 8 degrees and did the total advance timing at 2800 rpm, but to no avail I replaced the cap for the distributor I'm at a loss.
Drifting
Joined: Oct 2020
Posts: 1,560
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From: Wisconsin
Definitely run down any carb issues first (because it’s easier), but you might have a fuel pump on its way out.
Edit: I think Eddy carbs are very sensitive to fuel pressure; others more knowledgeable on here can fill you in on that.
Edit: I think Eddy carbs are very sensitive to fuel pressure; others more knowledgeable on here can fill you in on that.
Race Director
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From: Sunshine Coast, Queensland, Australia
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Cruise-In VIII Veteran
Well who put that Edlebrock on there and why? It should have been jetted up back when installed.
Has the car sat for extended periods with fuel in it?
Could the jets and circuits be particularly plugged with varnish?
Has the car sat for extended periods with fuel in it?
Could the jets and circuits be particularly plugged with varnish?
Thread Starter
Cruising
Joined: Oct 2023
Posts: 12
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From: New york
Race Director
Joined: Nov 2006
Posts: 12,937
Likes: 7,571
From: Sunshine Coast, Queensland, Australia
2025 C3 of the Year Finalist - Modified
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Cruise-In VIII Veteran
A lot more to set than just float height.
Contact Lars about properly rebuilding the correct carburetor for your car is the best advice I can give you.
Contact Lars about properly rebuilding the correct carburetor for your car is the best advice I can give you.
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Drifting
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From: Wisconsin
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Check out my YouTube channel, it's @Tunnelramlife in my playlists I have a section for Edelbrock carbs. Hope that helps
https://youtu.be/SUCbywN_3RY?si=HuSApfvsWbmT5QfY
https://youtu.be/SUCbywN_3RY?si=HuSApfvsWbmT5QfY
Drifting
Joined: Oct 2020
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From: Wisconsin
I suspect any carb expert will tell you to heave that Eddy carb into the nearest circular file. Eddy carbs don’t get much love as they are essentially a copy of a very old Carter design, and are OK at best for performance. Heck, I’ve still got a 1406 (square bore version) that came in a box with my car and I couldn’t give it away.
A well set up Quadrajet is a superior carb in all aspects. Hint: there’s a reason GM bolted millions of them on vehicles from the 60’s to the 80’s.
That said, many perceived carb problems are actually ignition problems. So, follow others’ advice and contact Lars for his white papers on tuning ignition and carbs.
A well set up Quadrajet is a superior carb in all aspects. Hint: there’s a reason GM bolted millions of them on vehicles from the 60’s to the 80’s.
That said, many perceived carb problems are actually ignition problems. So, follow others’ advice and contact Lars for his white papers on tuning ignition and carbs.
Tech Contributor
Joined: Aug 1999
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From: At my Bar drinking and wrenching in Lafayette Colorado
Backfire through the carb is a lean condition. That so-called "Edelbrock 1405" is nothing but a re-pop of the old, obsolete Carter AFB from 1964, which was deemed obsolete by GM after 1966. Through the miracle of Edelbrock marketing, that junk carb is now a "performance carb."
Get the right Q-Jet carb for your car and get it set up right. Use that old, undersized AFB carb to practice your hook-shots into the garage trash can, or spend the time and money to get it richened up so you can at least get your engine to transition off idle without a lean-pop backfire...
Get the right Q-Jet carb for your car and get it set up right. Use that old, undersized AFB carb to practice your hook-shots into the garage trash can, or spend the time and money to get it richened up so you can at least get your engine to transition off idle without a lean-pop backfire...
Le Mans Master
Joined: May 2007
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From: North tonawanda NY
My car came with a new polished elelbrock carb which had a lean stumble off Idle. I also had flooding issues till I installed a regulator and dialed the fuel pressure down to around 4psi. Eventually I replaced it with a holley then the quick fuel carb I have now with an AFR gauge for tuning.
Team Owner
Joined: Jan 2006
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From: Crossville TN
8 degrees timing at idle should be with the vacuum advance disconnected and the vacuum line plugged. When you reconnect that line the vacuum will advance timing significantly.
Even with that done, the factory specs for timing at that time jplaced the engine in a "retarded" condition (for what it really wanted or needed). Even an L-48 ran much better with 12 degrees BTDC timing at idle (with vacuum advance removed).
See if advancing your timing 3-4 degrees will eliminate your problem.
Even with that done, the factory specs for timing at that time jplaced the engine in a "retarded" condition (for what it really wanted or needed). Even an L-48 ran much better with 12 degrees BTDC timing at idle (with vacuum advance removed).
See if advancing your timing 3-4 degrees will eliminate your problem.
Drifting
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From: Wisconsin
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Le Mans Master
Joined: Aug 2017
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From: Cool Northern Michigan
Been there. Awful feeling. I lost three lobes years ago, before I knew about the missing Zinc from the motor oil story
For what it's worth and if you stick with a flat tappet next time, Comp Cams has a new F.T. lifter.
It has a coating on the base called Diamond Like Carbon. DLC
Supposed to end lobe wear from previous multiple faults: Wrong oil, improper break-in, too high of valve-spring rate, etc, etc, etc.
Part # CCA-812D -16
$124
Comps web site has more detail on the lifter. I just installed a set last week. The base of the lifter is almost black. Like black chrome.
For what it's worth and if you stick with a flat tappet next time, Comp Cams has a new F.T. lifter.
It has a coating on the base called Diamond Like Carbon. DLC
Supposed to end lobe wear from previous multiple faults: Wrong oil, improper break-in, too high of valve-spring rate, etc, etc, etc.
Part # CCA-812D -16
$124
Comps web site has more detail on the lifter. I just installed a set last week. The base of the lifter is almost black. Like black chrome.