Backfires under hard acceleration - Team Camaro Tech
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post #1 of 7 (permalink) Old Oct 2nd, 04, 11:37 AM Thread Starter
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Hey, i replace my intake manifold and carburetor a little while ago on my 67 camaro (350 c.i.). I just found out that when I floor it or accelerate quickly, there are some little backfires that come out of the carburetor. I am currently running a 650 speed demon carburetor with a vaccuum secondary. Can anyone explain what I might have to do to prevent the backfiring?

Thanks, Samuel

1967 Camaro SS. See pictures of it here: <a href="http://community.webshots.com/user/sbwell1020" target="_blank">http://community.webshots.com/user/sbwell1020</a>
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post #2 of 7 (permalink) Old Oct 2nd, 04, 02:41 PM
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Check for a flat lobe on the camshaft, your discription is text book for this condition. [img]graemlins/sad.gif[/img]
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post #3 of 7 (permalink) Old Oct 3rd, 04, 06:15 AM
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What intake and carb did you have on your car before you changed? What intake did you replace the old one with? Sounds like you could be running a touch on the lean side. That will give you popping from the carb as well. Any other details of your combo and your tune-up always help.
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post #4 of 7 (permalink) Old Oct 3rd, 04, 08:18 AM
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1. Ignition. Check your cap, rotor, wires and plugs to make sure you have a strong spark.

2. Too Lean. While you are checking the plugs look for little black specs on the insulator. If you see them you have some detonation and the engine may be running too lean or you have too much timing. If the insulator is pure white than that is also a good indication you may be too lean -- common this time of the year with good fall air.

3. Flat Lobe. Pull a valve cover and look to see if there are any loose rocker arms of rockers that don't move up and down as much as the others when cranking the engine.

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68 Camaro, E85 powered 427" small block. 9.96 @ 133 MPH, 1.319 sixty foot on motor. 5.92 eighth @ 116 with a 1.42 sixty breaking beams with back tire on the bottle
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post #5 of 7 (permalink) Old Oct 3rd, 04, 09:38 AM
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check for vacum leak around the intake.


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post #6 of 7 (permalink) Old Oct 3rd, 04, 12:22 PM Thread Starter
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I was previously running a stock intake manifold and stock rochester q-jet 4bbl. I replaced them with victor jr. and 650 speed demon vac. secondary.

1967 Camaro SS. See pictures of it here: <a href="http://community.webshots.com/user/sbwell1020" target="_blank">http://community.webshots.com/user/sbwell1020</a>
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post #7 of 7 (permalink) Old Oct 3rd, 04, 01:51 PM
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You might have to play with the accelerator pump calibration to get it to leave without popping back (if that is the problem). You might have to go with a smaller accelerator pump squirter . . . if it has a #31 try using a #28.

Is the rest of your engine stock? What other changes have you made to the motor?

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68 Camaro, E85 powered 427" small block. 9.96 @ 133 MPH, 1.319 sixty foot on motor. 5.92 eighth @ 116 with a 1.42 sixty breaking beams with back tire on the bottle
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