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Old 12-09-2006, 09:42 PM
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Erratic Idle and Backfire

I have a '70 Camaro Z28 motor installed in a '68 Corvette. Mods are Elgin Pro Stock cam, 242 int. 254 exh. @ .050. Comp Cams Magnum rockers, Holley 3310 750 CFM on an Edelbrock Performer spread bore manifold with Edelbrock adapter plate. MSD Pro Billit tach drive distributor running a Ford ignition box which drives a Jacobs ignition computer. Static timing is 12 btdc. Keith Black pistons with 10.2:1 compression. All the rest is stock Z28 350. My problem: On a cold start with the choke plate closed it cycles from 1000 to 2000 rpm regularly with about a two second cycle time and backfires through the left exaust. Timing stays steady at 12 btdc. If I pull off the vacuum advance hose it runs steady at about 1800 rpm with no backfire. After warm up it idles at 800 rpm with the vacuum advance connected. The carb hasn't been molested and it's one with the backfire protection for the power valve. I checked the 6.5 power valve with my Mity Vac and it's ok. I blew carb cleaner through the idle and high speed air bleeds. What am I overlooking?

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Old 12-10-2006, 04:55 AM
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check the diaphram on the distributor, sounds like it may be leaking vacuum.., or it may be carb idle related if ur hooked up on ported side
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Old 12-10-2006, 06:05 PM
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Put the Mity Vac on the vacuum advance. It's OK, holds vacuum and starts to advance at 8". Then I found that at 1200 RPM I have 12" of vacuum at the spark port on the Holley. I decided that it must be the carb so I swapped in an Edelbrock 1406 that I had. Problem gone! Now I'll have to put that Holley on the bench and check it out. The Edlebrock probably wont work right with my cam even if I could get the hood closed. In my first post I said that the timing was steady when the RPM was jumping around. I must have been looking at the damper cross eyed. I'll post again when I find the problem with the Holley.
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Old 12-13-2006, 07:20 PM
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Problem with the Holley was way too much Idle slot exposed at 800 RPM. Took a turn and a half on the secondary stop screw to crack them open just a tad. Put the Holley back on and rejusted idle mixture. Now the Holley likes my cam.
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Old 02-11-2009, 11:30 PM
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87 camaro z28 idle problems

my 87 z28 305 likes to idle high no matter what speed screw is at... but if i turn the speed screw too far it stalls...... im really confused, is it my carb? My dizzy or what???? please help
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Old 02-12-2009, 06:08 AM
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Quote:
Originally Posted by papabear88
my 87 z28 305 likes to idle high no matter what speed screw is at... but if i turn the speed screw too far it stalls...... im really confused, is it my carb? My dizzy or what???? please help
Ayuh,...Papabear,...

You'll get More,+ Better responces if you start your Own thread,...
Rather than tacking Your Problem onto a thread that's 3 Years Old...

The archives are for Readin',+ Learnin',.... Not posting too...

Btw,... Welcome Aboard,....

You didn't mention What your Carb is either....
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