Backfire Through Carb
Thread Starter
Instructor
Joined: Jun 2000
Posts: 113
Likes: 2
From: Austin Texas
Backfire Through Carb
Have '65 NOM 350 with an Edelbrock performer carb.
Just in the last few weeks it has started (what sounds to me like ) backfiring through the carb ever so slightly while driving. I can't repeat it when idleing in the the drive way. It's driving me crazy that I can't figure out what the problem is.
Assuming this is what's going on, then isn't this indicative of a lean condition? Isn't that fixed through the air/fuel mixture screws at the front of the carb?
If so - How would I adjust this? Something like turning them 3 turns and then 1/8 more or something?
If that isn't it, I have a suspicion that there may be a slight exhaust manifold leak - can that create the same sort of problem?
Thanks for any insight!
Just in the last few weeks it has started (what sounds to me like ) backfiring through the carb ever so slightly while driving. I can't repeat it when idleing in the the drive way. It's driving me crazy that I can't figure out what the problem is.
Assuming this is what's going on, then isn't this indicative of a lean condition? Isn't that fixed through the air/fuel mixture screws at the front of the carb?
If so - How would I adjust this? Something like turning them 3 turns and then 1/8 more or something?
If that isn't it, I have a suspicion that there may be a slight exhaust manifold leak - can that create the same sort of problem?
Thanks for any insight!
Race Director
Joined: Oct 2005
Posts: 12,470
Likes: 1,548
From: Camp Verde AZ
C1 of Year Finalist (performance mods) 2019
2017 C1 of Year Finalist
Lean.
Idle screws only work at idle. Jets take care of everything else, though you could have a dirty transition circuit depending on what throttle postion is.
Exhaust leaks only affect exhuast backfires. Do you have manifold or other vacuum leak, like a split hose or stuck PCV valve that is causing your problem?
Doug
Idle screws only work at idle. Jets take care of everything else, though you could have a dirty transition circuit depending on what throttle postion is.
Exhaust leaks only affect exhuast backfires. Do you have manifold or other vacuum leak, like a split hose or stuck PCV valve that is causing your problem?
Doug
Thread Starter
Instructor
Joined: Jun 2000
Posts: 113
Likes: 2
From: Austin Texas
You're right about the idle screw, that's air/fuel jets is what I meant. (Listen to what I mean, not what I say!!her. 
) Isn't the general adjustment three full turns & then another 1/8, or am I making that up?
I checked the vac hoses & they seem to be all right. Unless there's a leak between the carb & manifold, I don't think there's anything there, either.
Would an exhaust leak also make a sound similar to a slight carb backfire? Like I say, it only occurs when I'm driving and take my foot off the gas.
) Isn't the general adjustment three full turns & then another 1/8, or am I making that up?I checked the vac hoses & they seem to be all right. Unless there's a leak between the carb & manifold, I don't think there's anything there, either.
Would an exhaust leak also make a sound similar to a slight carb backfire? Like I say, it only occurs when I'm driving and take my foot off the gas.
Le Mans Master
Joined: Jul 2000
Posts: 8,506
Likes: 3
From: Calhoun, GA_______ Let It Rock
I had a similar problem. Lots of good info in this thread:
http://forums.corvetteforum.com/show...um_id=4&arch=1
http://forums.corvetteforum.com/show...um_id=4&arch=1
Safety Car
Joined: Feb 1999
Posts: 3,631
Likes: 14
From: Fountain Hills AZ
Originally Posted by Silver '65
Would an exhaust leak also make a sound similar to a slight carb backfire? Like I say, it only occurs when I'm driving and take my foot off the gas.
Burning Brakes
Joined: Jan 2006
Posts: 844
Likes: 2
From: Westminster Maryland
St. Jude Donor '08
Originally Posted by Silver '65
Have '65 NOM 350 with an Edelbrock performer carb.
Just in the last few weeks it has started (what sounds to me like ) backfiring through the carb ever so slightly while driving. I can't repeat it when idleing in the the drive way. It's driving me crazy that I can't figure out what the problem is.
Assuming this is what's going on, then isn't this indicative of a lean condition? Isn't that fixed through the air/fuel mixture screws at the front of the carb?
If so - How would I adjust this? Something like turning them 3 turns and then 1/8 more or something?
If that isn't it, I have a suspicion that there may be a slight exhaust manifold leak - can that create the same sort of problem?
Thanks for any insight!
Just in the last few weeks it has started (what sounds to me like ) backfiring through the carb ever so slightly while driving. I can't repeat it when idleing in the the drive way. It's driving me crazy that I can't figure out what the problem is.
Assuming this is what's going on, then isn't this indicative of a lean condition? Isn't that fixed through the air/fuel mixture screws at the front of the carb?
If so - How would I adjust this? Something like turning them 3 turns and then 1/8 more or something?
If that isn't it, I have a suspicion that there may be a slight exhaust manifold leak - can that create the same sort of problem?
Thanks for any insight!
Team Owner
Joined: Oct 2000
Posts: 38,897
Likes: 1,926
From: Washington Michigan
Originally Posted by Silver '65
Isn't the general adjustment three full turns & then another 1/8, or am I making that up? Would an exhaust leak also make a sound similar to a slight carb backfire? Like I say, it only occurs when I'm driving and take my foot off the gas.
When you take your foot off the gas while driving down the road, you are instantly feeding fuel to the engine from the idle system (not from the main metering system); if the idle mixture adjustment is too lean, you'll get afterfiring.
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