idle mixture - The 1947 - Present Chevrolet & GMC Truck Message Board Network

76bonanza · 03-12-2006, 09:34 PM

When adjusting the idle mixture screws is it best to take the vaccum reading from carb or intake? Just wondering if it matters.

**clay68c10** · 03-12-2006, 10:40 PM

Whatever gives you full manifold vacuum. I think it's easiest to go off the brake booster line. Some of the carb lines may be ported vacuum for timing advance, EGR or whatever.

76bonanza · 03-12-2006, 10:58 PM

ya I normal use the full vaccum off the carb but just wondering if it would be better off the rear intake port.

Karl Hoh · 03-12-2006, 11:51 PM

The rear intake port or anywhere on the manifold below the throttle blades will give you a true vacuum reading.

qksilver · 03-12-2006, 11:54 PM

Make sure your timing is set right and points dwell too, before you try to adjust the idle mixture. You will have to reset the idle speed.
You can also set the idle mixture by going for the highest idle speed when turning the screws

76bonanza · 03-13-2006, 12:02 AM

No points qksilver HEI. I find it is easier to set with a vaccum gauge. I think I will just pull the hose going to the tranny on the manifold and hook up there.

MDC · 03-13-2006, 01:35 AM

Quote:

Originally Posted by 76bonanza

No points qksilver HEI. I find it is easier to set with a vaccum gauge. I think I will just pull the hose going to the tranny on the manifold and hook up there.

That should be good. Anything below the butterflies should give you full manifold vaccuum.

03-12-2006, 09:34 PM	#1
76bonanza Senior Member Join Date: Mar 2003 Location: St robert Mo Posts: 2,001	idle mixture When adjusting the idle mixture screws is it best to take the vaccum reading from carb or intake? Just wondering if it matters. __________________ 1968 c10 lowered 3" 4" 355/Th400 built by Hatfield racing in joplin MO

03-12-2006, 10:40 PM	#2
clay68c10 Senior Member Join Date: Aug 2004 Location: Centennial, CO Posts: 2,935	Re: idle mixture Whatever gives you full manifold vacuum. I think it's easiest to go off the brake booster line. Some of the carb lines may be ported vacuum for timing advance, EGR or whatever. __________________ ClusterTruck: 68 C10 Bought in 89, wrecked in 03. Slow low $ rebuild started '17. 6.0 & TKO http://67-72chevytrucks.com/vboard/s...d.php?t=788602 93 K1500 Short Step, 350, NV4500, EBL flash ECU. Vortec heads & roller cam someday... 05 Jeep Wrangler Unlimited. 3” lift & 6-speed 02 E320 the insurance total “free car” 13 Tahoe LTZ

03-12-2006, 10:58 PM	#3
76bonanza Senior Member Join Date: Mar 2003 Location: St robert Mo Posts: 2,001	Re: idle mixture ya I normal use the full vaccum off the carb but just wondering if it would be better off the rear intake port. __________________ 1968 c10 lowered 3" 4" 355/Th400 built by Hatfield racing in joplin MO

03-12-2006, 11:51 PM	#4
Karl Hoh A little east of nowhere Join Date: Feb 2006 Location: LaBroquerie,Manitoba Canada Posts: 168	Re: idle mixture The rear intake port or anywhere on the manifold below the throttle blades will give you a true vacuum reading.

03-12-2006, 11:54 PM	#5
qksilver Senior Member Join Date: Dec 2004 Location: Southern Pines NC Posts: 3,853	Re: idle mixture Make sure your timing is set right and points dwell too, before you try to adjust the idle mixture. You will have to reset the idle speed. You can also set the idle mixture by going for the highest idle speed when turning the screws

03-13-2006, 12:02 AM	#6
76bonanza Senior Member Join Date: Mar 2003 Location: St robert Mo Posts: 2,001	Re: idle mixture No points qksilver HEI. I find it is easier to set with a vaccum gauge. I think I will just pull the hose going to the tranny on the manifold and hook up there. __________________ 1968 c10 lowered 3" 4" 355/Th400 built by Hatfield racing in joplin MO

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