Holley High Idle Question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

76vandura · 11-01-2002, 05:25 PM

When I first start my van, it idles really high. Somewhere between 1500-1800. It seems way to high. I have a holley 600 cfm carb on it. I am pretty sure it is the 4150 model. It has always done this since I put the carb on new. I think it is time to fix it! Any ideas?

76vandura · 11-01-2002, 05:58 PM

Also, one other thing. If I just touch the gas, the idle will shoot to 1200 and not return down to 800 until I kick it down with the pedal. I can't get it to idle smooth under 800. I have a small cam in the van, nothing lopey. Cam specs are:
SUM-K1102
Advertised duration: 262/272 deg
Duration @ .050": 204/214 deg
Lift: .420/.442

BigRed · 11-02-2002, 12:32 AM

I have the same carb on my '75 pickup and it does the exact same thing. I can't attest to the RPMs as I have not tach, but it sounds about right. I'd like to hear someone's take on this too!

79BIG10 · 11-02-2002, 04:25 AM

A few things come to mind. Retun spring not tight enough, choke not set correctly, stuck linkage (gunk in linkage). On the idle not being smooth how is the timing set? Sounds like timing may be off as well as maybe carb needs tuned to even out air flow in carb.

79Silv4x4 · 11-02-2002, 05:11 AM

Does it have an adjustable fast idle cam? I had to adjust this on my edelbrock 1406 due to the same problem.

*Piston* · 11-03-2002, 04:11 AM

Most of your automatic chokes on V8's are set to run the fast idle @ 1500-1700 rpm, a tap on the gas pedal will bring it down to 1200 or so.

On any holley automatic choke you can adjust the fast idle by using a small flat blade screw driver OR a 1/4" wrench. This fast idle screw is in a terrible spot really... Have someone sit inside the vehicle with thier foot on the gas (full throttle and engine OFF) while you adjust the screw. Locate the choke housing on the right side of the carb, look towards the base of this housing near the throttle linkage. You'll see a lever with a bolt going through... this is the fast idle adjustment. Keep in mind, every 1/4 turn of the screw = roughly 200rpm.

Now set the choke on its highest setting, let off the gas and start the engine. Your fast idle should be 1500-1800 on the highest setting. Of course you can set it anywhere you like.

Sorry I dont have a pic, I'll see if I can round one up if anyone cant find what im describing

11-01-2002, 05:25 PM	#1
76vandura Registered User Join Date: Sep 2002 Location: Cambridge, OH Posts: 64	Holley High Idle Question When I first start my van, it idles really high. Somewhere between 1500-1800. It seems way to high. I have a holley 600 cfm carb on it. I am pretty sure it is the 4150 model. It has always done this since I put the carb on new. I think it is time to fix it! Any ideas? __________________ 76 Gmc Vandura Custom, RIP 82 K30 4x4 6" Lift, Built 350, many mods 84 cutlass 350 chevy out of my vandura

11-01-2002, 05:58 PM	#2
76vandura Registered User Join Date: Sep 2002 Location: Cambridge, OH Posts: 64	Also, one other thing. If I just touch the gas, the idle will shoot to 1200 and not return down to 800 until I kick it down with the pedal. I can't get it to idle smooth under 800. I have a small cam in the van, nothing lopey. Cam specs are: SUM-K1102 Advertised duration: 262/272 deg Duration @ .050": 204/214 deg Lift: .420/.442 __________________ 76 Gmc Vandura Custom, RIP 82 K30 4x4 6" Lift, Built 350, many mods 84 cutlass 350 chevy out of my vandura Last edited by 76vandura; 11-01-2002 at 06:12 PM.

11-02-2002, 12:32 AM	#3
BigRed Registered User Join Date: Jun 2002 Location: DFW, TX Posts: 1,680	I have the same carb on my '75 pickup and it does the exact same thing. I can't attest to the RPMs as I have not tach, but it sounds about right. I'd like to hear someone's take on this too! __________________ Scott Shelbourne

11-02-2002, 04:25 AM	#4
79BIG10 I'm back with 2nd truck! Join Date: Feb 2002 Location: Texas Posts: 3,774	A few things come to mind. Retun spring not tight enough, choke not set correctly, stuck linkage (gunk in linkage). On the idle not being smooth how is the timing set? Sounds like timing may be off as well as maybe carb needs tuned to even out air flow in carb. __________________ 1979 Chevrolet Bonanza Big10 "Tootsie Roll" 1985 Chevrolet Silverado (wife's) Member of the Southern Bowties Club "Don't underestimate how sexy a fat man who drinks to excess can be." Homer Simpson

11-02-2002, 05:11 AM	#5
79Silv4x4 Workaholic Join Date: Oct 2002 Location: Katy, TX Posts: 1,589	Does it have an adjustable fast idle cam? I had to adjust this on my edelbrock 1406 due to the same problem. __________________ 1979 K-10 Silverado (work in progress) 1991 V1500 Subruban 1999 Suburban LT 4x4 2006 Suburban LTZ (daily driver)

11-03-2002, 04:11 AM	#6
Piston Account Suspended Join Date: Oct 2002 Location: Olathe, KS Posts: 2,300	Most of your automatic chokes on V8's are set to run the fast idle @ 1500-1700 rpm, a tap on the gas pedal will bring it down to 1200 or so. On any holley automatic choke you can adjust the fast idle by using a small flat blade screw driver OR a 1/4" wrench. This fast idle screw is in a terrible spot really... Have someone sit inside the vehicle with thier foot on the gas (full throttle and engine OFF) while you adjust the screw. Locate the choke housing on the right side of the carb, look towards the base of this housing near the throttle linkage. You'll see a lever with a bolt going through... this is the fast idle adjustment. Keep in mind, every 1/4 turn of the screw = roughly 200rpm. Now set the choke on its highest setting, let off the gas and start the engine. Your fast idle should be 1500-1800 on the highest setting. Of course you can set it anywhere you like. Sorry I dont have a pic, I'll see if I can round one up if anyone cant find what im describing

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