chevelle backfiring at acceleration
+4
ant7377
Brainstain
JiMi_DRiX
BlackChevelleSS
8 posters
G3GM :: G3 Tech :: Engine & Driveline
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chevelle backfiring at acceleration
Well, every weekend now Ive been driving my 73 chevelle ss sbc 350, holley 600, new plugs and wires, idles great and has been running really well, last night it done fine too. well today I go for a spin in it, and its backfiring at acceleration, I mean I barley push the gas down at all and it will backfire sounds like its coming from under the hood, if I just ease the peddle down it will be ok but I have to go very slow or it backfires and almost dies, but it still idles just fine and I can rev it up just fine and sounds great, just seems like its only doing this under load. Im still on stock points. Im hoping this is an easy fix like maybe just up grading to hei. any help would be great thanks.
Dead Man- G3GM Member
- Street Cred : 4
Re: chevelle backfiring at acceleration
check timing first, also check the dwell. if its still backfiring, need to check the cam make sure its not going flat
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BlackChevelleSS- Management
- Street Cred : 20
Re: chevelle backfiring at acceleration
Does it just continully back fire or just when you first step on the gas then it goes away and is normal?
ant7377- G3GM Addict
- Street Cred : 36
Re: chevelle backfiring at acceleration
First question: is it back0firing through the intake, or the exhaust ??
One item you can check is the distributor cap, for carbon tracks, where spark may be jumping between the terminals, and maybe the rotor for cracks.
Of course if it's running lean, like fuel-starved, it will back-fire through the carb.
Have you ever checked the fuel filter ?? Have an inline filter on that fuel line to the Holley ?? You could disconnect the line from the carb, spin it over with the starter & catch the fuel, to see how much the fuel pump is putting out (with the wire from the coil pulled out of the dist first).. If it's pumping plenty of fuel, you will have to assume that the fuel pump is OK......
Converting to an HEI distributor is the best idea, since you still have a point type. Nothing to do with your problem in my opinion.....unless that old coil is giving up.....
One item you can check is the distributor cap, for carbon tracks, where spark may be jumping between the terminals, and maybe the rotor for cracks.
Of course if it's running lean, like fuel-starved, it will back-fire through the carb.
Have you ever checked the fuel filter ?? Have an inline filter on that fuel line to the Holley ?? You could disconnect the line from the carb, spin it over with the starter & catch the fuel, to see how much the fuel pump is putting out (with the wire from the coil pulled out of the dist first).. If it's pumping plenty of fuel, you will have to assume that the fuel pump is OK......
Converting to an HEI distributor is the best idea, since you still have a point type. Nothing to do with your problem in my opinion.....unless that old coil is giving up.....
pila- Donating Member
- Street Cred : 43
Re: chevelle backfiring at acceleration
well if I step on it kinda fast it will do it but if I just ease into it, its ok. but no matter what speed im at it will do it if I put it down to fast. other than in park then it will rev just fine and as fast as I want it.but no not one pop after another just once right when I throttle it to fast. ( even though I wouldnt call it fast at all because if your not going down with it super slow it will pop.)ant7377 wrote:Does it just continully back fire or just when you first step on the gas then it goes away and is normal?
Dead Man- G3GM Member
- Street Cred : 4
Re: chevelle backfiring at acceleration
Im assuming its coming from the carb because its under the hood for sure. no fuel filter under the hood going to the carb, I going to add one of those now you mention it. but I will check and spin it over make sure its pumping good.pila wrote:First question: is it back0firing through the intake, or the exhaust ??
One item you can check is the distributor cap, for carbon tracks, where spark may be jumping between the terminals, and maybe the rotor for cracks.
Of course if it's running lean, like fuel-starved, it will back-fire through the carb.
Have you ever checked the fuel filter ?? Have an inline filter on that fuel line to the Holley ?? You could disconnect the line from the carb, spin it over with the starter & catch the fuel, to see how much the fuel pump is putting out (with the wire from the coil pulled out of the dist first).. If it's pumping plenty of fuel, you will have to assume that the fuel pump is OK......
Converting to an HEI distributor is the best idea, since you still have a point type. Nothing to do with your problem in my opinion.....unless that old coil is giving up.....
Dead Man- G3GM Member
- Street Cred : 4
Re: chevelle backfiring at acceleration
Pushing the pedal down slowly lets the fuel that's available, keep up with the engine, while pushing hard requires more fuel to accelerate, so it does kinda sound like a fuel problem.....
Maybe some debris in the carb, if there's no inline filter....
Maybe some debris in the carb, if there's no inline filter....
pila- Donating Member
- Street Cred : 43
Re: chevelle backfiring at acceleration
makes sense, I will check that tomorrow with day light, any thought on why it only does it under load though/while in gear.pila wrote:Pushing the pedal down slowly lets the fuel that's available, keep up with the engine, while pushing hard requires more fuel to accelerate, so it does kinda sound like a fuel problem.....
Maybe some debris in the carb, if there's no inline filter....
Dead Man- G3GM Member
- Street Cred : 4
Re: chevelle backfiring at acceleration
I have a similar problem with the 75 I bought, it had been sitting a while, so I'm thinking its related to that. Maybe a gummed up carb or something. I havent had time to try and diagnose it yet.
JiMi_DRiX- G3GM Enthusiast
- Street Cred : 3
Re: chevelle backfiring at acceleration
73ssbb wrote:well if I step on it kinda fast it will do it but if I just ease into it, its ok. but no matter what speed im at it will do it if I put it down to fast. other than in park then it will rev just fine and as fast as I want it.but no not one pop after another just once right when I throttle it to fast. ( even though I wouldnt call it fast at all because if your not going down with it super slow it will pop.)ant7377 wrote:Does it just continully back fire or just when you first step on the gas then it goes away and is normal?
What kind of carburetor do you have? It sounds like your accelerator pump on the carb might be a little out of adjustment and the backfire you hear is just a lean pop.
ant7377- G3GM Addict
- Street Cred : 36
Re: chevelle backfiring at acceleration
Sounds like a carb issue to me. I'm having almost the exact same problem with the 76 I just bought.
Brainstain- Donating Member
- Street Cred : 8
Re: chevelle backfiring at acceleration
If you have a holley heres something that can help you
https://www.youtube.com/watch?v=w3F3ssOb8lg
https://www.youtube.com/watch?v=w3F3ssOb8lg
ant7377- G3GM Addict
- Street Cred : 36
Re: chevelle backfiring at acceleration
A q-jet will have to have the top open and the little cup on the accelerator pump rod (goes up and down on the right front of the carb) you usually will see fuel around the little pocket there.
ant7377- G3GM Addict
- Street Cred : 36
Re: chevelle backfiring at acceleration
thank for the link, at the 250 mark in that vid it sounds just like mine, so it looks like I have some checking to do. it just bugs me that it was running just fine the night before lol. Only thing different in the vid is mine will only pop liek that while in gear, park and neutral it revs up fine with no problems.ant7377 wrote:If you have a holley heres something that can help you
https://www.youtube.com/watch?v=w3F3ssOb8lg
Dead Man- G3GM Member
- Street Cred : 4
Re: chevelle backfiring at acceleration
The inline fuel filter is a good idea as Pila said even if it has nothing to do with your issue.
77mali- Donating Member
- Street Cred : 62
Re: chevelle backfiring at acceleration
oh yeah, gonna do that first thing
Dead Man- G3GM Member
- Street Cred : 4
Re: chevelle backfiring at acceleration
73ssbb wrote:thank for the link, at the 250 mark in that vid it sounds just like mine, so it looks like I have some checking to do. it just bugs me that it was running just fine the night before lol. Only thing different in the vid is mine will only pop liek that while in gear, park and neutral it revs up fine with no problems.ant7377 wrote:If you have a holley heres something that can help you
https://www.youtube.com/watch?v=w3F3ssOb8lg
Yeah but go under the hood take off the air cleaner and listen carefully while you move the throttle bracket gently just get it past the accelerator pump.I bet you hear it go lean a little (sound like its sucking air) . Do you see in the video the pump cams? Maybe the little screw backed out and the arm isnt moving correctly or the bolt adjustment backed off (again this is all based on if you are running a holley but you get the idea its all similar) . Look down in the carb with the car off and see if you see gas shoot as soon as you move the throttle bracket (you should) .
ant7377- G3GM Addict
- Street Cred : 36
Re: chevelle backfiring at acceleration
yes its a holley 600, will check it out tomorrow with some updates. thanks guys
Dead Man- G3GM Member
- Street Cred : 4
Re: chevelle backfiring at acceleration
Update, it is backfiring in park after all, I took the breather off and reved it by hand to see if it was spraying gas like it should and it seems to be spraying just fine, but when I rev it hard it backfires through the carb I can see a flash of fire from the front part of the carb, the accelerator pump seems to be fine.
Dead Man- G3GM Member
- Street Cred : 4
Re: chevelle backfiring at acceleration
another update, went by my grandfathers body shop and told him what was going on so he wanted to check it out, we revved it, drove it like we stole it grandma the car ext ext, and it would not backfire at all it seems magically fine now.
Dead Man- G3GM Member
- Street Cred : 4
Re: chevelle backfiring at acceleration
Check to make sure your distributor hasnt moved. It sounds like it may be out quite a bit. Look at your ignition system,maybe the coil is starting to go bad. You have a backfire but do you have a miss while its running? Im still thinking its a fuel issue.
ant7377- G3GM Addict
- Street Cred : 36
Re: chevelle backfiring at acceleration
no miss it runs really well and strong.I think im gonna get a new fuel pump with hei upgrade if it acts up again. but I agree I think its a fuel problem.
Dead Man- G3GM Member
- Street Cred : 4
Re: chevelle backfiring at acceleration
well put the filter on today and it only backfired once, but its still doing it here and there, so guess Its time for the hei upgrade and go from there.
Dead Man- G3GM Member
- Street Cred : 4
Re: chevelle backfiring at acceleration
Maybe put in a fuel treatment like Gum Out or Seafoam w/ a freash tank of gas & see if it stops altogether. It might have just been the gas...you never know.
77mali- Donating Member
- Street Cred : 62
Re: chevelle backfiring at acceleration
Check your vacuum plugs, and base of carb. you may have developed a vacuum leak causing a lean backfire.. Increase in airflow with no increase in fuel flow will cause a lean backfire.
Bruisr- G3GM Member
- Street Cred : 8
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