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03-30-2014, 02:06 PM | #1 |
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Join Date: Apr 2012
Location: Henderson Nevada
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Backfire or Afterfire ?
1969 chevy 350,overhauled quadrajet carb,new pertronix ignition system. I will get up to speed around 55mph. Then all of the sudden a loss of power and POW! I believe out the exhuast and then picks up and gose like normal. Dosen't do it all the time just when I get on the highway. Runs good at all other conditions.
I have the carb mount directly to the cast iron manifold with a stainless steel shim, then a gasket then the carb. I have a divorced choke set up. Idle is set to spec.The ignition system is a pertronix set to spec. Any Ideas?
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1972 cheverolet K5 CST Blazer 350/auto/AC/PS/PB/Aux Batt From Medford, Oregon |
03-30-2014, 02:43 PM | #2 |
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Location: Tucson, AZ USA
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Re: Backfire or Afterfire ?
Pertronix Ignitor, Ignitor II or III? Flame-Thrower [I, II or III] Coil?
Did you run a new 10 or 12 ga. power lead from the tap in the Fuse block to the distributor (+), bypassing the stock Yellow 20 ga line? If not when the Yellow 20/Orange/Purple/White wire heats up, its resistance increases, dropping voltage down to 9VDC from 12VDC.
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Every 25 years I like to rebuild that 292, whether it needs it or not. |
03-30-2014, 03:03 PM | #3 |
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Location: South Westerlo, New York
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Re: Backfire or Afterfire ?
X2, sounds like you're loosing spark for a milisecond and when it catches again its burning the unignited gas, back in the day we would reach over and turn the ignition key off and back on to whom ever was driving, one time we held it too long and it split his muffler wide open...
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Thanks, Joe.. 1969 C/10, 348 C.I., 3X2 bbl. V8, 2004r , LWB. |
03-30-2014, 03:57 PM | #4 | |
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Re: Backfire or Afterfire ?
Quote:
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1972 cheverolet K5 CST Blazer 350/auto/AC/PS/PB/Aux Batt From Medford, Oregon Last edited by asolde; 03-30-2014 at 04:14 PM. |
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03-30-2014, 05:25 PM | #5 |
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Location: Junction City, KS
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Re: Backfire or Afterfire ?
Sound like your carb couldbr overloading, running a bit rich. I had one doing that a few years back.
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Joseph Joe's 69 GMC http://67-72chevytrucks.com/vboard/s...d.php?t=543253 1969 GMC SWB-350 SBC 700R4 2013 Ram 2500 CC Laramie Longhorn Edition-6.7 PPEI EFI Live CSP5 5” ProFlo Exhaust |
03-30-2014, 06:46 PM | #6 |
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Location: South Westerlo, New York
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Re: Backfire or Afterfire ?
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Thanks, Joe.. 1969 C/10, 348 C.I., 3X2 bbl. V8, 2004r , LWB. |
03-31-2014, 08:57 PM | #7 | |
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Location: Tucson, AZ USA
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Re: Backfire or Afterfire ?
Quote:
Today I did accidently kick my Red 10 ga. lead off the terminal in traffic to the HEI for the 350 V8 in '71 GMC Jimmy. I dead-sticked off the road and after 5 minutes troubleshooting found the gremlin and reconnected it. Good to go. A little more pressure with some needlenose pliers and it won't happen again. Some people hard wire them. I treat it like a truck, not a Boeing 777.
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Every 25 years I like to rebuild that 292, whether it needs it or not. |
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04-07-2014, 08:27 PM | #8 |
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Location: Henderson Nevada
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Re: Backfire or Afterfire ?
Update I ran the 12 ga red wire from the fuse blk to my coil and it was a good soild fix. Thxs Alex
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1972 cheverolet K5 CST Blazer 350/auto/AC/PS/PB/Aux Batt From Medford, Oregon |
04-08-2014, 01:29 AM | #9 |
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Join Date: Feb 2002
Location: Tucson, AZ USA
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Re: Backfire or Afterfire ?
Cool, Brother.
Glad to be of help.
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Every 25 years I like to rebuild that 292, whether it needs it or not. |
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