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01-29-2008, 04:46 AM
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#1 |
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Senior Member
 
Join Date: Jan 2002
Location: Williston, ND
Posts: 2,999
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engine question
I have a 72 chevy shortbox with a 402 out of a 70 gmc. It has an HEI setup in it. It will idle fine, but when you rev it up it will backfire. It has a new fuel pump. Is there anything I can check. Thanks
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68 Chevy CST/10, 50th Anniversary, 327/th400, 373 posi, buckets 68 GMC Shortbox Stepside, 402/th400, Tilt, Tach, Bucket Seats, 3.08 Positraction 69 Chevy Camaro SS, 383, 4 speed, positraction 70 Chevy El Camino SS396, Triple Black, 454/th400, Tach 70 Chevy Shortbox Stepside 4x4, 350/th350, Tilt, Tach, Cab Lights, Bumper Guards, Tow Hooks 70 Chevy 3/4 Longbox, 350/auto, 70k, SURVIVOR 71 Chevy Blazer, CST, 350/auto 71 GMC Sierra K2500, 454, 4 speed, 4.10 posi, 37s 71 Custom/30, Open Road, 350/th400, tilt 72 Chevy Shortbox Fleetside, 496 Stroker/th400, Tilt, Tach, Bucket Seats, 3.42 Posi 72 GMC Sierra Grande 2500. 427/th400, tilt, a/c, tool and stowage, buckets/console, 3.54 posi |
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01-29-2008, 05:34 AM
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#2 |
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its all about the +6 inches
Join Date: Jan 2001
Location: Hilliard Ohio
Posts: 2,690
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Re: engine question
is the timing set properly?
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01-29-2008, 08:18 AM
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#3 |
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Registered User
Join Date: Feb 2006
Location: San Diego
Posts: 631
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Re: engine question
Check spark plugs wires are on the right plugs and carb for missing caps on vacuum ports.
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01-29-2008, 09:11 AM
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#4 |
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Registered User
Join Date: Jan 2007
Location: South Florida
Posts: 158
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Re: engine question
Timing ???
Rob |
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01-29-2008, 09:23 AM
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#5 |
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To The Levy
Join Date: Jan 2007
Location: california
Posts: 391
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Re: engine question
Dont forget to look for a flat cam, I would deffinately look at the firing order like listed above, not too retarded on timing and cap isnt crossfiring, (water in cap) if all the basics are fine, put you a vacuum gauge on a manifold source and verify steady vacuum readings at idle and cruise, if you having a bouncy needle, you may be lookin at either a broken valve spring, rocker prob. or flat cam. good luck
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01-29-2008, 09:51 AM
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#6 |
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Senior Member
 
Join Date: Sep 2005
Location: Lewisville, Nc
Posts: 10,238
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Re: engine question
timing?
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David fuller Ase Certified Mechanic Click here to help support our board!! 1971 Chevy c-10 under going a 4.8l LSx swap Build Thread http://67-72chevytrucks.com/vboard/s...d.php?t=421305 2007 Honda Accord my daily 145kmiles 2002 Honda Accord 4 door With 330k(sisters car) 2005 toyota Avalon 228k( brothers car) 2002 Sububran 5.3 245k 2000 Tahoe 5.3l 378 General manager for Marco's Carwash & lube |
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01-29-2008, 10:51 AM
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#7 |
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Registered User
Join Date: Jul 2007
Location: Salina, Kansas
Posts: 1,998
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Re: engine question
i had a backfiring problem on my 72 402 big block....autozone told me to set my new spark plugs to .035 gap...so i did and it back fired like a son of a gun...so i checked my old plug and it was at .040.......so id check your spark plug gap...if that aint it like the guys said its prolly your timing.....i had it back firing again only when it was cold and my choke was bad so it could be your choke possibly
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