Backfiring through Carb/Dieseling after shutoff.
#1
Thread Starter
Junior Member
Joined: Jan 2024
Posts: 23
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From: Fayetteville, Arkansas
Car: 1984 Camaro Z/28
Engine: L69 -> L31
Transmission: 700R4
Axle/Gears: 3.42
Backfiring through Carb/Dieseling after shutoff.
I am stumped on the mystery of my engine. Whenever I get the total timing at 36*, the engine is sluggish at times and backfires through the carb and diesels after I shut it off. When I advance it a little more, the backfiring goes away but still diesels. When I retard it, dieseling goes away but backfires more often. I feel like its either/or if I want to be able to drive it.
I have swapped a crate L31 with a Lunati 20080660 cam, a Holley Street Warrior with the default fuel mixture (1.5 screw turns from lightly seated), and a Electric 7psi Edelbrock fuel pump to get fuel to the carb. I am also using Autolite Iridium XP sparkplugs.
I appreciate the help and feel free to ask questions.
I have swapped a crate L31 with a Lunati 20080660 cam, a Holley Street Warrior with the default fuel mixture (1.5 screw turns from lightly seated), and a Electric 7psi Edelbrock fuel pump to get fuel to the carb. I am also using Autolite Iridium XP sparkplugs.
I appreciate the help and feel free to ask questions.
#2
Re: Backfiring through Carb/Dieseling after shutoff.
Whenever this scenario arises, it is usually a good idea to verify the timing marks with the actual mechanical TDC of the engine. A new crank, new balancer, new timing cover and tab, and other variables can result in the timing marks being WAY off actual piston TDC.
#3
Joined: Nov 2008
Posts: 2,022
Likes: 155
From: Milwaukee
Car: 92 Firebird, 77 Trans Am SE, 86 Z28
Engine: 5.7 HSR, T/A 6.6, empty
Transmission: T-5, TH350, T-5
Axle/Gears: 3.08 posi, 3.23 posi, 3.23
Re: Backfiring through Carb/Dieseling after shutoff.
There's a lot that's capable to be to blame but just a random thought, is the fuel fresh?
#4
Thread Starter
Junior Member
Joined: Jan 2024
Posts: 23
Likes: 0
From: Fayetteville, Arkansas
Car: 1984 Camaro Z/28
Engine: L69 -> L31
Transmission: 700R4
Axle/Gears: 3.42
#5
Joined: Nov 2008
Posts: 2,022
Likes: 155
From: Milwaukee
Car: 92 Firebird, 77 Trans Am SE, 86 Z28
Engine: 5.7 HSR, T/A 6.6, empty
Transmission: T-5, TH350, T-5
Axle/Gears: 3.08 posi, 3.23 posi, 3.23
Re: Backfiring through Carb/Dieseling after shutoff.
What happens when you bump the octane up? What's compression?
#6
Thread Starter
Junior Member
Joined: Jan 2024
Posts: 23
Likes: 0
From: Fayetteville, Arkansas
Car: 1984 Camaro Z/28
Engine: L69 -> L31
Transmission: 700R4
Axle/Gears: 3.42
#7
Joined: Nov 2008
Posts: 2,022
Likes: 155
From: Milwaukee
Car: 92 Firebird, 77 Trans Am SE, 86 Z28
Engine: 5.7 HSR, T/A 6.6, empty
Transmission: T-5, TH350, T-5
Axle/Gears: 3.08 posi, 3.23 posi, 3.23
Re: Backfiring through Carb/Dieseling after shutoff.
Did you have this engine running before the cam? Did you degree the cam to check and see if it is what it claims to be? Just tossing out ideas since the list of possibilities isn't exactly short. I wouldn't rely on the timing marks to confirm what degree its at, that's for sure. Verification of that will help, but the number itself isn't important if the engine is happy.
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#8
Thread Starter
Junior Member
Joined: Jan 2024
Posts: 23
Likes: 0
From: Fayetteville, Arkansas
Car: 1984 Camaro Z/28
Engine: L69 -> L31
Transmission: 700R4
Axle/Gears: 3.42
Re: Backfiring through Carb/Dieseling after shutoff.
Did you have this engine running before the cam? Did you degree the cam to check and see if it is what it claims to be? Just tossing out ideas since the list of possibilities isn't exactly short. I wouldn't rely on the timing marks to confirm what degree it’s at, that's for sure. Verification of that will help, but the number itself isn't important if the engine is happy.
#9
Joined: Nov 2008
Posts: 2,022
Likes: 155
From: Milwaukee
Car: 92 Firebird, 77 Trans Am SE, 86 Z28
Engine: 5.7 HSR, T/A 6.6, empty
Transmission: T-5, TH350, T-5
Axle/Gears: 3.08 posi, 3.23 posi, 3.23
Re: Backfiring through Carb/Dieseling after shutoff.
then I wouldn't trust the mechanicals in the least. Me personally, I'd take the whole thing apart.
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