67 Camaro Back Firing Up Through Carb!!! - Team Camaro Tech
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post #1 of 17 (permalink) Old Feb 2nd, 06, 04:13 PM Thread Starter
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Question 67 Camaro Back Firing Up Through Carb!!!

My 67 Camaro with the original 350 motor, has always back fired a bit out of the carb. Well atleast since i've owned it. Since i bought it 5 years ago, i haven't driven it all that much. Cause it's been in and out of the shop for paint, interior, etc. I didn't re-build the engine though. So what would cause the engine to back fire out the carb, and not out the tail pipes? Thanks.

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post #2 of 17 (permalink) Old Feb 2nd, 06, 06:28 PM
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Re: 67 Camaro Back Firing Up Through Carb!!!

Top of the list,

Bad accelerator pump

Flat cam

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post #3 of 17 (permalink) Old Feb 2nd, 06, 06:33 PM Thread Starter
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Re: 67 Camaro Back Firing Up Through Carb!!!

Quote:
Originally Posted by dyno jonn
Top of the list,

Bad accelerator pump

Flat cam
It's a new carb, Holley 600 cfm. And the cam is stock. I'm not very tech savey when it comes it to mechanical stuff. Can you gimmie some details please? Thanks.

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post #4 of 17 (permalink) Old Feb 2nd, 06, 06:37 PM
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Re: 67 Camaro Back Firing Up Through Carb!!!

Have you set the timing correct?


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post #5 of 17 (permalink) Old Feb 2nd, 06, 06:55 PM Thread Starter
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Re: 67 Camaro Back Firing Up Through Carb!!!

Quote:
Originally Posted by WaynesWorld
Have you set the timing correct?
Someone else told me to check my timing too. It's at the shop right now getting new suspension put in. I guess i'll have them check that also. Thanks for the advice!

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post #6 of 17 (permalink) Old Feb 2nd, 06, 07:33 PM
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Re: 67 Camaro Back Firing Up Through Carb!!!

Timing could be way advanced or a sticky intake valve. possible weak or broken valve spring. More than likely a flat cam would keep the intake valve closed and it would not backfire through the carb. Cam timing could be off, jumped time or a plastic gear used is worn? First thing I would do is compression check, then check it for TDC and set timing. After that tune it if no other problems are found. It could be a vacume leak also.

Do the compression check first then move on to other things. Eliminate mechanical problems first.

Joe

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post #7 of 17 (permalink) Old Feb 2nd, 06, 10:20 PM
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Re: 67 Camaro Back Firing Up Through Carb!!!

Backfire through the carb is a sure sign of a lean condition. Often it is caused by an accellerator pump problem making it difficult to transition from the idle slots to the main jets without a lean backfire. A manifold leak can cause it also. Unless the carb isn't quite setup, I'd suspect the vacuum leak first. You shouldn't have to tweak a new 600cfm carb that much to get it to run right. Sounds like you've got a serious issue that goes beyond the carb.

Verify the firing order is 1.8.4.3.6.5.7.2 and check for carbon tracks on the inside of the distributor cap that could be causing cross-fire.

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post #8 of 17 (permalink) Old Feb 3rd, 06, 04:59 AM
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Re: 67 Camaro Back Firing Up Through Carb!!!

Quote:
More than likely a flat cam would keep the intake valve closed and it would not backfire through the carb.
I should have been more specific. A flat exhaust lobe on a cam can cause a backfire through the carb. I even saw one Q-jet carb melted on the inside because the car had been driven so long with a flat cam. That cam had 5 lobes that looked like fuel pump lobes. Little old lady didn't have it looked at till the car would barely run.

Another thing that you don't see anymore, but was common in the late 60's early 70's, was when original equiptment double wall exhaust pipes would collapse on the inside causing much the same symptoms.

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post #9 of 17 (permalink) Old Feb 3rd, 06, 11:40 AM Thread Starter
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Re: 67 Camaro Back Firing Up Through Carb!!!

Whoa, looks like i better tackle this sooner than later. So i'll have my compresion and timing checked. If it's not that, i might be in the market for a crate motor. Cause who knows what else is down the road. Then i can go through this engine and work out all the kinks. Thanks fellas!

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post #10 of 17 (permalink) Old Feb 3rd, 06, 12:25 PM
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Re: 67 Camaro Back Firing Up Through Carb!!!

Make sure you check the carb and as stated above check for vacume leaks, it could just be a lean condition. Don't rush out and buy a new engine if you don't need to, but they are tempting!!

Joe

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post #11 of 17 (permalink) Old Feb 4th, 06, 10:24 AM Thread Starter
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Re: 67 Camaro Back Firing Up Through Carb!!!

Quote:
Originally Posted by Joe Harrison
Make sure you check the carb and as stated above check for vacume leaks, it could just be a lean condition. Don't rush out and buy a new engine if you don't need to, but they are tempting!!

Joe
I'm gonna have it looked over on Monday. Hopefully it's something minor. But, the engine had this problem before i upgraded the carb, intake manifold, and fuel pump. Originaly when i got the car, it had a 69 Z/28 intake manifold, 750 Rochester off of a 67 SS 396 Camaro, and stock fuel pump. And it back fired then. Now i've got a Holley 600cfm Carb, Edelbrock Performer intake, and a Holley High Volume Fuel Pump. And i replaced the stock distributor to a MSD HEI Distributor, a MSD Blaster 2 Coil, and a MSD 6A Ignition Box. So we'll see.

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post #12 of 17 (permalink) Old Feb 14th, 06, 08:11 PM
 
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Re: 67 Camaro Back Firing Up Through Carb!!!

sounds like it's time to make a new cam selection to me. just my 2 cents worth. mabe a busted valve spring?
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post #13 of 17 (permalink) Old Feb 16th, 06, 08:29 AM
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Re: 67 Camaro Back Firing Up Through Carb!!!

Good feedback above.

Usually backfire though the carb is a timing issue, but a broken vavle spring will cause it as well.

A vacuum leak usually causes backfires through the exhaust.

When does she backfire,..on start up?..acceleration?...deceleration? Also, does she ever diesel (run-on after ignition is turned off)?
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post #14 of 17 (permalink) Old Feb 16th, 06, 06:18 PM Thread Starter
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Re: 67 Camaro Back Firing Up Through Carb!!!

Quote:
Originally Posted by Straight-line-69
Good feedback above.

Usually backfire though the carb is a timing issue, but a broken vavle spring will cause it as well.

A vacuum leak usually causes backfires through the exhaust.

When does she backfire,..on start up?..acceleration?...deceleration? Also, does she ever diesel (run-on after ignition is turned off)?
Well my mechanic said one of the spark plug boots was melted to the spark plug. So he cut the wire back, and put on a new boot. He said it seemed to run fine after that.

The car mostly back fired up through the carb when it was cold, upon acceleration. When i gave it gas quick, it would back fire. I'd then have to ease the throttle, then it was okay. But still didn't run as good as it should. Before i changed out everything(ignition, intake, carb, etc.), it would run for a second or two after i shut it off. Doesn't do it anymore. We'll see after i get it back on Monday. Keep the input comin'! I don't think i'm outta the woods yet on this one.

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post #15 of 17 (permalink) Old Feb 16th, 06, 06:57 PM
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Re: 67 Camaro Back Firing Up Through Carb!!!

Depending on your carb, you might also want to consider checking the power valve. Backfires through the carb usually kill the power valve.


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