Help! Unstable Idle
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Joined: Jun 2003
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From: Placedo TX
Help! Unstable Idle
Starting to do some PM to my 1964 327/365 Stingray. Used JonhZ's procedure on setting the valve lash. Also put in some new Autolite plugs gapped at .045. New air cleaner & had the Holley 600cfm carb. rebuilt last week. Timing is around 12 deg. advanced.- Seems that the idle is very unstable, if I set it at 900rpm its fine till the first time I rev it up- it seems to rev back down to around 1400rpm & stabilizes at that rpm. If I adjust the carb.idle adjust.screw out it will idle down to 900 rpm but after awhile it seems that it will idle very low around 500 rpm. Then I adjust the idle back up to 900 & gas it and then the cycle begins again. I checked the throttle linkage & its not in a bind- whatsoever. The manual choke has been wired open & the vaccum secondaries seem to be closed. Could the dual point mallory dist. cause this? I checked the dwell today & with only the ignition on it was at about 30 deg. but if I turned the car on it was reading about 5 deg & the car would idle very low & eventually would cut off. Running out of ideas. Any suggestions? 
[Modified by 1quik6, 10:27 PM 6/26/2004]
[Modified by 1quik6, 10:29 PM 6/26/2004]
[Modified by 1quik6, 11:54 PM 6/26/2004]
[Modified by 1quik6, 10:27 PM 6/26/2004]
[Modified by 1quik6, 10:29 PM 6/26/2004]
[Modified by 1quik6, 11:54 PM 6/26/2004]
Team Owner
Joined: Oct 2000
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From: Washington Michigan
Re: Help! Unstable Idle (1quik6)
Gap your plugs at .035", not .045". Your idle is unstable because you don't have a functioning vacuum advance system that's fully deployed at idle; you're idling "on the curve" of the centrifugal advance system in the distributor. Trash the non-vacuum advance Mallory dual-point distributor (lots of people on eBay who don't know any better will want it), and replace it with a stock Delco vacuum advance distributor, with an Echlin #VC-1810 vacuum advance can ($10 at NAPA), connected to full manifold vacuum. End of problem. 
Le Mans Master
Joined: Mar 1999
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From: delmont pa
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Re: Help! Unstable Idle (1quik6)
also make sure the advance weights in the distributor are returning all the way. sticking advance weights will cause your problem. this even happens in GM distributors 
Pro
Joined: Feb 2000
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From: knoxville tn
Re: Help! Unstable Idle (clem zahrobsky)
I had this same problem on my 66 350hp after engine rebuild with stock gm cam. found an article in ncrs corvette restorer mag. that suggested a vacuum advance unit from bumper to bumper auto parts chain. after installation problem solved. I'm sure other chains sell the same or similar unit.
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Joined: Jun 2003
Posts: 82
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From: Placedo TX
Re: Help! Unstable Idle (vettefool)
The dual points are on the top plate & the springs seem to be under them. Is it possible to take the top plate off & maybe clean & lubricate the weights & springs? Does the non-vaccum dist.'s have an advantage over the vaccum dist's.? HP?
Thanks In Advance
1QUIK6
Thanks In Advance
1QUIK6
Le Mans Master
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From: delmont pa
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Re: Help! Unstable Idle (1quik6)
i am sure you can remove the top plate and get to the springs and weights. a vacuum advance distributor will give you much better gas milage than the one you have and the performance will be the same
