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Holley 390 CFM idles too fast

Tiny
VMAXX85
  • MEMBER
  • 1979 JEEP CJ5
  • 4.2L
  • 6 CYL
  • 4WD
  • MANUAL
  • 56,000 MILES
Installed Offenhauser intake and Holley 390 CFM 4bbl. Cant get it to Idle below 1,000 rpm's. Curb idle screw not touching stop. Distributor vac line to ported vac on carburetor. Checked for vac leaks and tightened all intake bolts. Checked with for leaks with brake cleaner then re-tightened bolts.
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Saturday, November 30th, 2019 AT 8:54 PM

9 Replies

Tiny
ASEMASTER6371
  • MECHANIC
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Good morning,

If the idle stop screw is all the way backed off and you have no vacuum leaks, I would remove the carburetor and look at the throttle plates and make sure they are fully closed and not open just a small amount. You can adjust the plates with the 2 screws on the Throttle shaft.

Roy
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Sunday, December 1st, 2019 AT 5:43 AM
Tiny
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Okay, thanks. I will try that next and let you know how it turns out.
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Sunday, December 1st, 2019 AT 9:32 AM
Tiny
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You are welcome.

Keep me updated.

Roy
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Sunday, December 1st, 2019 AT 9:50 AM
Tiny
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I took carburetor off, flipped it over. Secondary's closed completely, but primaries open about 16th and primary adjustment screw about 1/8 from contacting screw. Manipulated throttle several times and notices slight bind then primary closed completely and primary adjustment screw contacted stop. Reproduced this binding and release several times. Noticed choke fast idle screw seemed to be catching between end of screw and red plastic fast idle cam. Cam seems loose on its pivot and end of screw doesn't contact squarely on any of the steps. Put carburetor back on and started up engine. It fast idles at around 1,500 or so but wont kick off fast idle with a throttle quick blip. It will drop off fast idle by hand removing from fast idle cam but still idles at 1000K with curb idle screw in contact with stop.
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Sunday, December 1st, 2019 AT 11:32 AM
Tiny
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Your issue is the binding you have. What did you do about the binding?

Roy
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Sunday, December 1st, 2019 AT 12:01 PM
Tiny
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I didn't fix the binding, I think the choke assembly may be at fault. I suppose I will remove the choke assy (electric) to determine if the binding is caused by its mechanism, If not i'm unsure where to proceed.
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Sunday, December 1st, 2019 AT 12:10 PM
Tiny
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Just back off the high idle screw all the way and make sure the idle comes down.

Do that first.

Roy
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Sunday, December 1st, 2019 AT 12:23 PM
Tiny
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K, Ill give that a try tomorrow, and keep you posted, thanks Forrest
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Sunday, December 1st, 2019 AT 4:41 PM
Tiny
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You are welcome.

Always glad to help.

Roy
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Sunday, December 1st, 2019 AT 4:44 PM

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