vacuum advance ?'s - The 1947 - Present Chevrolet & GMC Truck Message Board Network

67 LWB · 05-31-2004, 05:29 PM

I need some help with figuring if my vacuum advance is hooked up to the the right port. I have a HEI and a quadrajet. Is it supposed to have vacuum at idle or no vacuum? Right now the port it is hooked up to has no vacuum at idle and on up. Isn't there supposed to be some vacuum to advance the distributor? Thanks for the help.

Devin

crazy longhorn · 05-31-2004, 05:48 PM

Q jet, with HEI should be hooked to no vac port @ idle.....with that said, you should know that this was for emissions control! you can get a crane adjustable vac advance, & follow the instruction for a good "recurve" (crane reccomends to run manifold vac to the dist can. If you are running a stock cam , either way should work for you(try em both, & see what works better in your particular app). IMHO, manifold vac is the way to go, but will for sure require a recurve on your dist. they all tune/time a little differently(depending on combo), but remember the 60'S hypo stuff ran MANIFOLD vac to the dist can

the vac advance is more of a "load sensing device", & the vac retards the timing under low rpm /hy load situations. A sb chev will handle as much as 52 degrees timing under part throttle loads....but the little mill will only like 32-36 degrees @ full throttle @ wide open throttle. Best of luck,crazyL

67 LWB · 05-31-2004, 06:19 PM

ok, thanks for the reply crazy longhorn.

71-longbed · 05-31-2004, 06:22 PM

ive got a crane adjustable canister ... im running advance (vacuum) at idle ... i dont notice any problems... im under the impression that you get better gas mileage that way .. its more effiecent at idle ..so to speak ...
i also installed the springs that came with the kit ... 1 silver and 1 blue .... im gonna tweak around with it more this summer ...

good luck

franko72 · 05-31-2004, 08:09 PM

how can you test the vacuum advance to see if it is functioning correctly.My truck doesnt respond well out of the hole. Could the Vac. advance be the culprit if it wasnt working right?

Jeepster376 · 05-31-2004, 08:36 PM

Put the line on a manifold vacuum port while the engine is running, and you're RPMs should jump up.

Jeepster376 · 05-31-2004, 08:42 PM

Quote:

Originally Posted by franko72

how can you test the vacuum advance to see if it is functioning correctly.My truck doesnt respond well out of the hole. Could the Vac. advance be the culprit if it wasnt working right?

Vac advance works mainly increasing advance during low and part throttle driving. If you tromp on it, the vacuum drops and the vac advance returns the timing back to it's mechanical setting. You may notice a better throttle response, but not greater full throttle out of the hole acceleration.

Jeepster376 · 05-31-2004, 08:46 PM

If I remember right the ported vaccum, was for the purpose of reducing emissions during closed throttle deceleration. I don't think it is for benefit during idle.

franko72 · 06-01-2004, 07:43 PM

Thanks jeepster ,I tried connecting it straight to maniloldand and the RPMs increased. That must mean that the advance is working.

05-31-2004, 05:29 PM	#1
67 LWB Registered User Join Date: Jan 2002 Location: COLORADO SPRINGS Posts: 102	vacuum advance ?'s I need some help with figuring if my vacuum advance is hooked up to the the right port. I have a HEI and a quadrajet. Is it supposed to have vacuum at idle or no vacuum? Right now the port it is hooked up to has no vacuum at idle and on up. Isn't there supposed to be some vacuum to advance the distributor? Thanks for the help. Devin __________________ '67 C10 LWB FLEETSIDE, WEAK 305 , TH400, 3.73 REAR COLORADO SPRINGS, CO.

05-31-2004, 05:48 PM	#2
crazy longhorn Fabricate till you "puke" Join Date: Jun 2002 Location: Ill Posts: 9,403	Q jet, with HEI should be hooked to no vac port @ idle.....with that said, you should know that this was for emissions control! you can get a crane adjustable vac advance, & follow the instruction for a good "recurve" (crane reccomends to run manifold vac to the dist can. If you are running a stock cam , either way should work for you(try em both, & see what works better in your particular app). IMHO, manifold vac is the way to go, but will for sure require a recurve on your dist. they all tune/time a little differently(depending on combo), but remember the 60'S hypo stuff ran MANIFOLD vac to the dist can the vac advance is more of a "load sensing device", & the vac retards the timing under low rpm /hy load situations. A sb chev will handle as much as 52 degrees timing under part throttle loads....but the little mill will only like 32-36 degrees @ full throttle @ wide open throttle. Best of luck,crazyL __________________ 69 longhorn,4" chop,3/5 drop, 1/2 ton suspension/disc brakes,1 1/2" body drop,steel tilt clip, 5.3/Edelbrock rpm intake/600 carb, Hooker streetrod shorties,2 1/2" exhaust/ H pipe/50's Flows , 6 spd Richmond trans,12 bolt/ 3.40 gears....

05-31-2004, 06:19 PM	#3
67 LWB Registered User Join Date: Jan 2002 Location: COLORADO SPRINGS Posts: 102	ok, thanks for the reply crazy longhorn. __________________ '67 C10 LWB FLEETSIDE, WEAK 305 , TH400, 3.73 REAR COLORADO SPRINGS, CO.

05-31-2004, 06:22 PM	#4
71-longbed Its Magically Delicious Join Date: Jan 2003 Location: oregon Posts: 2,398	ive got a crane adjustable canister ... im running advance (vacuum) at idle ... i dont notice any problems... im under the impression that you get better gas mileage that way .. its more effiecent at idle ..so to speak ... i also installed the springs that came with the kit ... 1 silver and 1 blue .... im gonna tweak around with it more this summer ... good luck __________________ 71 C10 LWB 350sbc -TH350 12 bolt 3.42 Posi Of all my favorite things to do, The utmost is to have a brew. My love grows for my foamy friend, with each thirst-quenching elbow bend. Beer so frosty, smooth, and cold it's paradise pure liquid gold. Yes beer means many things to me that's all for now cus I gotta pee.

05-31-2004, 08:09 PM	#5
franko72 Franko72 Join Date: May 2004 Location: Cincinnati,Ohio Posts: 471	how can you test the vacuum advance to see if it is functioning correctly.My truck doesnt respond well out of the hole. Could the Vac. advance be the culprit if it wasnt working right? __________________ 1972 C20 cheyenne Super 402 BB/400 turbo LWB A/C Tilt, Cruise Control, Saddle tanks, Tach My Home Page Better to burn out than it is to rust

05-31-2004, 08:36 PM	#6
Jeepster376 Registered User Join Date: Feb 2004 Location: Massachusetts Posts: 269	Put the line on a manifold vacuum port while the engine is running, and you're RPMs should jump up. __________________ 72 Cheyenne Super 4x4 SWB

05-31-2004, 08:46 PM	#8
Jeepster376 Registered User Join Date: Feb 2004 Location: Massachusetts Posts: 269	If I remember right the ported vaccum, was for the purpose of reducing emissions during closed throttle deceleration. I don't think it is for benefit during idle. __________________ 72 Cheyenne Super 4x4 SWB

06-01-2004, 07:43 PM	#9
franko72 Franko72 Join Date: May 2004 Location: Cincinnati,Ohio Posts: 471	Thanks jeepster ,I tried connecting it straight to maniloldand and the RPMs increased. That must mean that the advance is working. __________________ 1972 C20 cheyenne Super 402 BB/400 turbo LWB A/C Tilt, Cruise Control, Saddle tanks, Tach My Home Page Better to burn out than it is to rust



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