Carter AFB vacuum quesion - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Custom 68 · 04-29-2002, 12:53 PM

This may be a weird question but I have a Carter AFB carb with 2 vac lines on front one has zero vac at idle and goes up as I rev the motor and the other has vac til I rev then it goes to zero? Is this normal and which do I hook the vac advance to?
Thanks
Dave

Slick1 · 04-29-2002, 01:42 PM

that's normal. one port, (the one that has vacuum at idle) is tied directly to manifold vacuum. the other port is carburetor vacuum, so there is low vacuum there until you rev up the engine. Of course, when you rev the engine, the vacuum on the other port will go lower, as manifold vacuum decreases when accelerating, esp under a load. I prefer the carb vacuum for vacuum advance, although there are two schools of thought on this. Try 'em both, see which one you like the best.

dmnall · 04-29-2002, 06:21 PM

Wouldn't you want to hook up your Distributor to the Ported Vacuum Port, so you will run Vacuum Advance untill a certain rpm, then Mechanical Advance will take over ?? I hooked my HEI Dist. to ported Vacuum and I think that is the Left Port on the AFB??

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Truck #1 68 Chev LWB Fleet w/ Wood Floor (Sucks Gas and Hauls Ass!) and in process of Body Work...

Truck #2 1994 GMC Sierra SL w/ 4.3L Vortec V6, 4L60E Auto!!

69 longhorn · 04-29-2002, 06:33 PM

If you are runnin a hot cam & fat carburation,it will run best hooked to full manifold vac @ the carb. The 60s perf stuff was set up this way. Along with emissions came lean carbs,& ported spark.......69

Custom 68 · 04-29-2002, 08:08 PM

Thanks guys so when you say ported is that the one with vacuum on it at idle or the one without vac until I rev the motor. My Quad only had one vac port it was simple. I may just put it back on.

Who knows?
Thanks again
Dave

69 longhorn · 04-29-2002, 08:21 PM

ported is no vac @ idle.......69

04-29-2002, 06:21 PM	#3
dmnall Registered User Join Date: Apr 2001 Location: Goleta, CA Posts: 505	Wouldn't you want to hook up your Distributor to the Ported Vacuum Port, so you will run Vacuum Advance untill a certain rpm, then Mechanical Advance will take over ?? I hooked my HEI Dist. to ported Vacuum and I think that is the Left Port on the AFB?? ------------------ Truck #1 68 Chev LWB Fleet w/ Wood Floor (Sucks Gas and Hauls Ass!) and in process of Body Work... Truck #2 1994 GMC Sierra SL w/ 4.3L Vortec V6, 4L60E Auto!! __________________ 1968 C10 Truck LWB Fleetside 1968 C10 Truck SWB Stepside 1994 K2500 Ext Cab Fleetside 2008 Honda Civic Si lease

04-29-2002, 06:33 PM	#4
69 longhorn Registered User Join Date: Aug 2001 Location: rock island,il,usa Posts: 5,382	If you are runnin a hot cam & fat carburation,it will run best hooked to full manifold vac @ the carb. The 60s perf stuff was set up this way. Along with emissions came lean carbs,& ported spark.......69 __________________ http://community.webshots.com/user/hotrodhorn

04-29-2002, 08:08 PM	#5
Custom 68 Registered User Join Date: Nov 2001 Location: Springfield, MO Posts: 2,939	Thanks guys so when you say ported is that the one with vacuum on it at idle or the one without vac until I rev the motor. My Quad only had one vac port it was simple. I may just put it back on. Who knows? Thanks again Dave __________________ Dave 1968 Custom Chevy with turbo charged 5.3 gen III 4l80e swap 1967-71 GMC 3/4 ton long step 4x4 (not sure what year exactly?) "A good friend will bail you out of jail...but a true friend will be sitting next to you saying "that was frekin awesome". "If it doesn't fit force it...If it breaks then it needed to be replaced anyway!"

04-29-2002, 08:21 PM	#6
69 longhorn Registered User Join Date: Aug 2001 Location: rock island,il,usa Posts: 5,382	ported is no vac @ idle.......69 __________________ http://community.webshots.com/user/hotrodhorn

04-29-2002, 12:53 PM	#1
Custom 68 Registered User Join Date: Nov 2001 Location: Springfield, MO Posts: 2,939	Carter AFB vacuum quesion This may be a weird question but I have a Carter AFB carb with 2 vac lines on front one has zero vac at idle and goes up as I rev the motor and the other has vac til I rev then it goes to zero? Is this normal and which do I hook the vac advance to? Thanks Dave __________________ Dave 1968 Custom Chevy with turbo charged 5.3 gen III 4l80e swap 1967-71 GMC 3/4 ton long step 4x4 (not sure what year exactly?) "A good friend will bail you out of jail...but a true friend will be sitting next to you saying "that was frekin awesome". "If it doesn't fit force it...If it breaks then it needed to be replaced anyway!"

04-29-2002, 01:42 PM	#2
Slick1 Registered User Join Date: Mar 2002 Location: Olathe, Ks USA Posts: 29	that's normal. one port, (the one that has vacuum at idle) is tied directly to manifold vacuum. the other port is carburetor vacuum, so there is low vacuum there until you rev up the engine. Of course, when you rev the engine, the vacuum on the other port will go lower, as manifold vacuum decreases when accelerating, esp under a load. I prefer the carb vacuum for vacuum advance, although there are two schools of thought on this. Try 'em both, see which one you like the best.



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