Vaccum to Carburator

hercules72 · 10-03-2001, 11:05 AM

I have a 72 mustang with a 302 and a 2100 carburator. I only have one vaccum line going to the carb it is on the passenger side and it goes to the dist. If i hook a vaccum gauge up to it I have no pressure until i give it gas. Should i have more lines running to it also i am trying to work on the air/fuel mixture and i was told to put a vaccum gauge on it and use that. Can someone please help me get the vaccum lines running to the right place.

PKRWUD · 10-03-2001, 01:44 PM

There are two types of vacuum; manifold vacuum and ported vacuum. The vacuum port on the passenger side of the carb is ported vacuum. Ported vacuum increases with rpm, whereas manifold vacuum drops with rpm. The ported vacuum from your carb is used to control the vacuum advance in the distributor. So far, you have everything hooked up correctly. In order to use a vacuum gauge to set your mixture, you must find a manifold vacuum port. Look on the intake manifold, behind the carb. Once you find a source of manifold vacuum, attach the gauge to it and start the engine. Adjust the idle speed, and then start turning the mixture screws, slowly. It doesn't matter which way you turn them, as long as the vacuum gauge needle goes up. Switch back and forth between the adjusters until you reach the highest possible reading on the gauge. Now, turn the screws the other way until the needle just starts to fall. reset the idle speed. You're done.

Take care
~Chris

------------------
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73 Mustang Boy · 10-03-2001, 01:48 PM

The vaccum line you are checking is a timed vaccum line and should have litte to no vaccum when the car is idling. You need to be checking manifold vaccum which is greatest at idle and decreases as RPMs increase.Find a vaccum line coming straight out of the intake it will be manifold vaccum. The best way I know of to adjust the mixture is to run both idle screws all the way in and then back them out 3.5 turns. Then turn 1 screw out till the car starts to run rough then turn it in .25 of a turn. repeat with the other screw. This should have the idle mixture close to beeing right. If needed you can adjust the screws slightly from there to achieve highest manifold vaccum.

fastsvo · 10-05-2001, 02:04 PM

I used to have a vaccum line going from the back of the manifold (vacc. block) to the pass side of the carb (ported vac right?). This is a 2bbl btw. My mechanic blocked this off. Why? Can't base timing also affect the vaccum at idle? Wouldn't you have to make sure the timing is dead on, then start fiddling with the carb and a vacc. guage? I need a quick refresh on the basics on fine tuning the SB ford.

Rev · 10-06-2001, 08:15 PM

Can't figure any reason to connect a manifold vacuum to a ported vacuum (ventouri). Some Ford (dual port) distributors did have both ported and manifold connections. Avoid those things.

Manifold vacuum sources have uses and ported (ventouri)sources have other functions. Use the the correct vacuum source for what is indicated.

Rev

------------------
'66 Coupe, 306, 300 HP, C-4, 13.97 e.t., 100.3 mph
1/4 mi.

PKRWUD · 10-07-2001, 04:24 AM

fastsvo-
Not sure who was thinking what, but there was no point in connecting your vacuum hose that way. My suggestions above presumed that the timing was already set.

Take care
~Chris

------------------
Retired Moderator
MustangNet

My site: JimPorterRacing

RACECAR spelled backwards is RACECAR

HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

zach0 · 10-07-2001, 08:30 AM

Want to make sure I have mine right because I just bought a new 600cfm holley for my 289. Large vacuum line to PCV valve on Valve cover. Vacuum Line in rear manifold going to transmission. Air filter to valve cover.

------------------
66 Mustang Black W/ Black
289 Hi-Po 65'heads, MSD
Lunati High lift Cam
750CFM Carb Heddman Headers, Hurst Shifter

PKRWUD · 10-07-2001, 09:11 AM

Sounds good. If your distributor has vacuum advance, the little port on the passenger side of the carb, right above the idle mixture screw, is the one that goes to the distributor. Otherwise, cap it.

Take care
~Chris

------------------
Retired Moderator
MustangNet

My site: JimPorterRacing

RACECAR spelled backwards is RACECAR

HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

Kisner · 10-08-2001, 10:26 AM

Need same advice for my 68 coupe, 302, Edelbrock 600 cfm 4bl. My mechanic has one vacuum line running from distributor to front of carburator, another large line from middle front of carburator to driver side valve cover into PCV valve, passenger side valve cover is closed with oil cap (not using original breather), and another from manifold to transmission. After looking at original engine manual, I think the PCV valve may be on the wrong side or if it's even necessary to have. Manual leads me to believe originally fresh air was to enter driver side valve cover and exit through PCV valve on passenger side valve cover? Any help would be greatly appreciated.

PKRWUD · 10-08-2001, 01:02 PM

It doesn't matter which side has the PCV valve (which you should keep!). What does matter is that there is no location for filtered air to enter the crankcase. You need to have either a hose going from the air cleaner to the other valve cover, or a breather. You're sucking air out, but you're not replacing it. That will lead to more oil in the intake, and fouled plugs, etc.

Take care
~Chris

------------------
Retired Moderator
MustangNet

My site: JimPorterRacing

RACECAR spelled backwards is RACECAR

HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

Kisner · 10-09-2001, 10:25 AM

Any suggestions on how to hook up a hose to the chrome, round, aftermarket air cleaner I'm using? I know I can buy an original type oil cap with a built in nipple to hook the hose to going in the valve cover, but not sure how I'd hook it up to the air cleaner. Thanks.

10-03-2001, 11:05 AM	#1
hercules72 Registered Member Join Date: Jul 2001 Location: Grundy Center, Ia Posts: 4	Vaccum to Carburator I have a 72 mustang with a 302 and a 2100 carburator. I only have one vaccum line going to the carb it is on the passenger side and it goes to the dist. If i hook a vaccum gauge up to it I have no pressure until i give it gas. Should i have more lines running to it also i am trying to work on the air/fuel mixture and i was told to put a vaccum gauge on it and use that. Can someone please help me get the vaccum lines running to the right place.

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10-03-2001, 01:44 PM	#2
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	There are two types of vacuum; manifold vacuum and ported vacuum. The vacuum port on the passenger side of the carb is ported vacuum. Ported vacuum increases with rpm, whereas manifold vacuum drops with rpm. The ported vacuum from your carb is used to control the vacuum advance in the distributor. So far, you have everything hooked up correctly. In order to use a vacuum gauge to set your mixture, you must find a manifold vacuum port. Look on the intake manifold, behind the carb. Once you find a source of manifold vacuum, attach the gauge to it and start the engine. Adjust the idle speed, and then start turning the mixture screws, slowly. It doesn't matter which way you turn them, as long as the vacuum gauge needle goes up. Switch back and forth between the adjusters until you reach the highest possible reading on the gauge. Now, turn the screws the other way until the needle just starts to fall. reset the idle speed. You're done. Take care ~Chris ------------------ Retired Moderator MustangNet My site: JimPorterRacing RACECAR spelled backwards is RACECAR HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

10-03-2001, 01:48 PM	#3
73 Mustang Boy Registered Member Join Date: Aug 2001 Location: Georgia Posts: 84	The vaccum line you are checking is a timed vaccum line and should have litte to no vaccum when the car is idling. You need to be checking manifold vaccum which is greatest at idle and decreases as RPMs increase.Find a vaccum line coming straight out of the intake it will be manifold vaccum. The best way I know of to adjust the mixture is to run both idle screws all the way in and then back them out 3.5 turns. Then turn 1 screw out till the car starts to run rough then turn it in .25 of a turn. repeat with the other screw. This should have the idle mixture close to beeing right. If needed you can adjust the screws slightly from there to achieve highest manifold vaccum.

10-05-2001, 02:04 PM	#4
fastsvo Registered Member Join Date: Jul 1999 Posts: 44	I used to have a vaccum line going from the back of the manifold (vacc. block) to the pass side of the carb (ported vac right?). This is a 2bbl btw. My mechanic blocked this off. Why? Can't base timing also affect the vaccum at idle? Wouldn't you have to make sure the timing is dead on, then start fiddling with the carb and a vacc. guage? I need a quick refresh on the basics on fine tuning the SB ford.

10-06-2001, 08:15 PM	#5
Rev Registered Member Join Date: Nov 1998 Location: Houston, Tx. Posts: 3,887	Can't figure any reason to connect a manifold vacuum to a ported vacuum (ventouri). Some Ford (dual port) distributors did have both ported and manifold connections. Avoid those things. Manifold vacuum sources have uses and ported (ventouri)sources have other functions. Use the the correct vacuum source for what is indicated. Rev ------------------ '66 Coupe, 306, 300 HP, C-4, 13.97 e.t., 100.3 mph 1/4 mi.

10-07-2001, 04:24 AM	#6
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	fastsvo- Not sure who was thinking what, but there was no point in connecting your vacuum hose that way. My suggestions above presumed that the timing was already set. Take care ~Chris ------------------ Retired Moderator MustangNet My site: JimPorterRacing RACECAR spelled backwards is RACECAR HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

10-07-2001, 08:30 AM	#7
zach0 Registered Member Join Date: Apr 2001 Location: Hampton, Virginia Posts: 227	Want to make sure I have mine right because I just bought a new 600cfm holley for my 289. Large vacuum line to PCV valve on Valve cover. Vacuum Line in rear manifold going to transmission. Air filter to valve cover. ------------------ 66 Mustang Black W/ Black 289 Hi-Po 65'heads, MSD Lunati High lift Cam 750CFM Carb Heddman Headers, Hurst Shifter

10-07-2001, 09:11 AM	#8
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	Sounds good. If your distributor has vacuum advance, the little port on the passenger side of the carb, right above the idle mixture screw, is the one that goes to the distributor. Otherwise, cap it. Take care ~Chris ------------------ Retired Moderator MustangNet My site: JimPorterRacing RACECAR spelled backwards is RACECAR HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

10-08-2001, 10:26 AM	#9
Kisner Registered Member Join Date: Nov 2000 Posts: 290	Need same advice for my 68 coupe, 302, Edelbrock 600 cfm 4bl. My mechanic has one vacuum line running from distributor to front of carburator, another large line from middle front of carburator to driver side valve cover into PCV valve, passenger side valve cover is closed with oil cap (not using original breather), and another from manifold to transmission. After looking at original engine manual, I think the PCV valve may be on the wrong side or if it's even necessary to have. Manual leads me to believe originally fresh air was to enter driver side valve cover and exit through PCV valve on passenger side valve cover? Any help would be greatly appreciated.

10-08-2001, 01:02 PM	#10
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	It doesn't matter which side has the PCV valve (which you should keep!). What does matter is that there is no location for filtered air to enter the crankcase. You need to have either a hose going from the air cleaner to the other valve cover, or a breather. You're sucking air out, but you're not replacing it. That will lead to more oil in the intake, and fouled plugs, etc. Take care ~Chris ------------------ Retired Moderator MustangNet My site: JimPorterRacing RACECAR spelled backwards is RACECAR HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

10-09-2001, 10:25 AM	#11
Kisner Registered Member Join Date: Nov 2000 Posts: 290	Any suggestions on how to hook up a hose to the chrome, round, aftermarket air cleaner I'm using? I know I can buy an original type oil cap with a built in nipple to hook the hose to going in the valve cover, but not sure how I'd hook it up to the air cleaner. Thanks.