how to correctly use a vacuum guage.. - The 1947 - Present Chevrolet & GMC Truck Message Board Network

oldblue1968chevy · 08-20-2009, 05:50 PM

I bought a vacuum guage awhile back.....im not really sure how to use it. (I understand you plug it into the vacumn line,but which one) Ive heard you can tune your motor to get better mileage with it..

Can somebody tell me if I should keep it or return it or let it set in the box.

Shine some light on this subject please.

**john** · 08-20-2009, 05:56 PM

Heres a diagram chart.
http://www.classictruckshop.com/club...ts/vac/uum.htm

Jacfourteen · 08-20-2009, 06:01 PM

Quote:

Originally Posted by john

Heres a diagram chart.
http://www.classictruckshop.com/club...ts/vac/uum.htm

I forgot that you can use them as a diagnostic tool, I thought he was more interested in carb tuning since he mentioned milage. Oh yeah, you connect it to a vac port that has full vacuum (one that is on the intake manifold or one that is on the base plate of the carb)

Jacfourteen · 08-20-2009, 05:57 PM

you can use these to help tune the carb, mainly the idle mixture (and on holleys you use it to find what power valve to use). The specifics of how to use it depend on the carb you are running......so what you got?

oldblue1968chevy · 08-20-2009, 06:01 PM

edelbrock 500cfm electric choke (not hooked up though) its running nearly pefect.

Jacfourteen · 08-20-2009, 06:03 PM

sorry I'm more familiar with holleys, but I know that if you go to the edelbrock website you can find tuning guides in the tech section. Good luck!

mclairmo · 08-20-2009, 06:04 PM

I once hooked one up to my carb and taped it to my windshield so I could find out what power valve to use. Not too smart, would not do that again.

oldblue1968chevy · 08-20-2009, 06:04 PM

ok

Is it worth bothering with?
And which vacumn port do I plug it into?

68gmsee · 08-20-2009, 06:21 PM

If you have several vacuum ports look to see if you have below the butterfly valve- that's manifold vacuum and it's the one to use. Ported vacuum is above the butterfly valve.

Keep the gauge. I bought one many years ago and it sat in a box for several years. Then I started having problems with the carb and had to put a kit in it. Needless to say, the gauge came in handy again. I've used it several time since to refine the carb for maximum vacuum at idle.

Theoretically you can isolate different problems from bad valves to ignition problems with these gauges. I've ownly used it for carb adjustments.

mclairmo · 08-20-2009, 06:12 PM

Yes, it's worth it but you have to study the vacuum gauge directions and possibly consult a carb tuning guide to really understand how to use it. You would hook it up to full manifold vacuum, (i.e., below the carb throttle plates). It is a device for the person who really wants to spend some time tuning his engine and has the patience to really study it, IMO.

oldblue1968chevy · 08-20-2009, 06:14 PM

so its really not worth a 17 year olds time lol...id like to understand it but am not very good at carb. tuning lol

mclairmo · 08-20-2009, 06:18 PM

I consider it a somewhat esoteric tool for the carb tuning nerds that really want to make a study of it, like me. I like that kind of stuff but many backyard mechanics don't have the patience or the time to really understand how engine vacuum can be a window into how your engine is performing.

oldblue1968chevy · 08-20-2009, 06:24 PM

ok well if i go hook it up

ive got a hose going from dizzy to carb.(which would that be)

ive 1 port high on the left, and 1 low on the right (i THINK the dizzy goes to the lower one on the right)which one do i hook it to?

mclairmo · 08-20-2009, 06:31 PM

Lower is full manifold vacuum. However, if the vacuum advance canister was hooked up to it, you may need to use a T so you can keep vacuum going to the vacuum advance canister while you tune the carb up with the vacuum guage installed.

cparman · 08-20-2009, 07:27 PM

vacuum gauges can be a wonderful diagnostic tool if you let it.
you can use it to adjust timing, by watching the gauge and turning the distributor until you have your highest vacuum reading. Sometimes you will have a gas ping, and will need to back off the timing a bit

use it to know what power valve you need
diagnose a burned valve
make sure you have enough vacuum

play with it, understand it, the gauge is a powerful tool

mclairmo · 08-20-2009, 07:30 PM

"Luke, my son . . . may the vacuum force be with you."

oldblue1968chevy · 08-20-2009, 08:31 PM

Ok i'll try to play with the vacumn guage this weekend (gotta fix my wheeler first, so i can sell it to buy more stuff for the truck

so i want the most vacum reading on the guage as I can...without pinging GOTCHA

any more replys??...

TonyJohnson · 08-20-2009, 10:50 PM

When you're driving, they are also a good idicator of potential gas mileage. If you're running a lot of vacuum, your mileage will suck...

CG · 08-20-2009, 11:11 PM

Here's one I have, I got it off the 72 C10 Burb I gave to my son.

**'68OrangeSunshine** · 08-21-2009, 06:02 AM

This subject came up last year in a thread titled: _Vacuum Cluster_ by Its70 on 4/03/2008. Sorry I don't know how to link threads.
Anyway I use a vacuum gauge [Mooneyes 2-1/8"] in the dash of my daily driver. It tells me a lot about my engine's internal condition while moving. I have another hand-held Vac gauge in my tune up kit and we use it for tweaking up the carb.
It's a great instrument, once you get the hang of it.

08-20-2009, 05:50 PM	#1
oldblue1968chevy Grandpa in the rustmobile... Join Date: Nov 2008 Location: Spokane WA/Viola TN Posts: 11,422	how to correctly use a vacuum guage.. I bought a vacuum guage awhile back.....im not really sure how to use it. (I understand you plug it into the vacumn line,but which one) Ive heard you can tune your motor to get better mileage with it.. Can somebody tell me if I should keep it or return it or let it set in the box. Shine some light on this subject please. __________________ John Goose-1968 C10 355,9.32-1CR, Vortec Heads ,262 voodoo, 3.73:1 3OTT (HS ride/beater/farm truck) http://67-72chevytrucks.com/vboard/s...d.php?t=317684 Grams 53-1953 Chevrolet Belair http://67-72chevytrucks.com/vboard/s...=1#post4327784 1969 Chevy C10 Shortbed 4.5/6?" Frame off resto http://67-72chevytrucks.com/vboard/s...d.php?t=548136 1999 Toyota Tacoma 4x4

08-20-2009, 05:56 PM	#2
john member #16 Join Date: Dec 1999 Location: Yuba City Ca. Posts: 3,618	Re: how to correctly use a vacuum guage.. Heres a diagram chart. http://www.classictruckshop.com/club...ts/vac/uum.htm __________________ john http://67-72chevytrucks.com/vboard/showgroups.php board vendors http://www.flickr.com/photos/1745471...7602865984234/

08-20-2009, 05:57 PM	#4
Jacfourteen Big Red - Now its a SWB! Join Date: Jun 2009 Location: Oroville, Ca Posts: 1,624	Re: how to correctly use a vacuum guage.. you can use these to help tune the carb, mainly the idle mixture (and on holleys you use it to find what power valve to use). The specifics of how to use it depend on the carb you are running......so what you got? __________________ 68 3/4 ton (Project)-350 Small Block, .030 over, 10:1 comp, 3998993 heads, C3BX edelbrock intake, comp cams XE268, Holley 670 SA, long tube headers, dual flow 40's, E-fan, Alum rad, currently under the knife getting shortened and bagged build thread 41 3/4 ton (wife's)-flatbed, fully restored to original 01 Tahoe LT 4WD (my daily driver)-Magnaflow Muffler, Rollin on 22's 02 Ford Mustang Convertable (Wife's Car)-Flowmaster 50, Clear corners, Intake, sittin on 18's

08-20-2009, 06:01 PM	#5
oldblue1968chevy Grandpa in the rustmobile... Join Date: Nov 2008 Location: Spokane WA/Viola TN Posts: 11,422	Re: how to correctly use a vacuum guage.. edelbrock 500cfm electric choke (not hooked up though) its running nearly pefect. __________________ John Goose-1968 C10 355,9.32-1CR, Vortec Heads ,262 voodoo, 3.73:1 3OTT (HS ride/beater/farm truck) http://67-72chevytrucks.com/vboard/s...d.php?t=317684 Grams 53-1953 Chevrolet Belair http://67-72chevytrucks.com/vboard/s...=1#post4327784 1969 Chevy C10 Shortbed 4.5/6?" Frame off resto http://67-72chevytrucks.com/vboard/s...d.php?t=548136 1999 Toyota Tacoma 4x4

08-20-2009, 06:03 PM	#6
Jacfourteen Big Red - Now its a SWB! Join Date: Jun 2009 Location: Oroville, Ca Posts: 1,624	Re: how to correctly use a vacuum guage.. sorry I'm more familiar with holleys, but I know that if you go to the edelbrock website you can find tuning guides in the tech section. Good luck! __________________ 68 3/4 ton (Project)-350 Small Block, .030 over, 10:1 comp, 3998993 heads, C3BX edelbrock intake, comp cams XE268, Holley 670 SA, long tube headers, dual flow 40's, E-fan, Alum rad, currently under the knife getting shortened and bagged build thread 41 3/4 ton (wife's)-flatbed, fully restored to original 01 Tahoe LT 4WD (my daily driver)-Magnaflow Muffler, Rollin on 22's 02 Ford Mustang Convertable (Wife's Car)-Flowmaster 50, Clear corners, Intake, sittin on 18's

08-20-2009, 06:04 PM	#7
mclairmo Registered User Join Date: Jan 2006 Location: Take Off Posts: 1,908	Re: how to correctly use a vacuum guage.. I once hooked one up to my carb and taped it to my windshield so I could find out what power valve to use. Not too smart, would not do that again.

08-20-2009, 06:21 PM	#9
68gmsee Active Member Join Date: Jul 2007 Location: Centrally located between Houston, Austin and Waco. BCS area. Posts: 7,947	Re: how to correctly use a vacuum guage.. If you have several vacuum ports look to see if you have below the butterfly valve- that's manifold vacuum and it's the one to use. Ported vacuum is above the butterfly valve. Keep the gauge. I bought one many years ago and it sat in a box for several years. Then I started having problems with the carb and had to put a kit in it. Needless to say, the gauge came in handy again. I've used it several time since to refine the carb for maximum vacuum at idle. Theoretically you can isolate different problems from bad valves to ignition problems with these gauges. I've ownly used it for carb adjustments.

08-20-2009, 06:12 PM	#10
mclairmo Registered User Join Date: Jan 2006 Location: Take Off Posts: 1,908	Re: how to correctly use a vacuum guage.. Yes, it's worth it but you have to study the vacuum gauge directions and possibly consult a carb tuning guide to really understand how to use it. You would hook it up to full manifold vacuum, (i.e., below the carb throttle plates). It is a device for the person who really wants to spend some time tuning his engine and has the patience to really study it, IMO.

08-20-2009, 06:14 PM	#11
oldblue1968chevy Grandpa in the rustmobile... Join Date: Nov 2008 Location: Spokane WA/Viola TN Posts: 11,422	Re: how to correctly use a vacuum guage.. so its really not worth a 17 year olds time lol...id like to understand it but am not very good at carb. tuning lol __________________ John Goose-1968 C10 355,9.32-1CR, Vortec Heads ,262 voodoo, 3.73:1 3OTT (HS ride/beater/farm truck) http://67-72chevytrucks.com/vboard/s...d.php?t=317684 Grams 53-1953 Chevrolet Belair http://67-72chevytrucks.com/vboard/s...=1#post4327784 1969 Chevy C10 Shortbed 4.5/6?" Frame off resto http://67-72chevytrucks.com/vboard/s...d.php?t=548136 1999 Toyota Tacoma 4x4

08-20-2009, 06:18 PM	#12
mclairmo Registered User Join Date: Jan 2006 Location: Take Off Posts: 1,908	Re: how to correctly use a vacuum guage.. I consider it a somewhat esoteric tool for the carb tuning nerds that really want to make a study of it, like me. I like that kind of stuff but many backyard mechanics don't have the patience or the time to really understand how engine vacuum can be a window into how your engine is performing.

08-20-2009, 06:24 PM	#13
oldblue1968chevy Grandpa in the rustmobile... Join Date: Nov 2008 Location: Spokane WA/Viola TN Posts: 11,422	Re: how to correctly use a vacuum guage.. ok well if i go hook it up ive got a hose going from dizzy to carb.(which would that be) ive 1 port high on the left, and 1 low on the right (i THINK the dizzy goes to the lower one on the right)which one do i hook it to? __________________ John Goose-1968 C10 355,9.32-1CR, Vortec Heads ,262 voodoo, 3.73:1 3OTT (HS ride/beater/farm truck) http://67-72chevytrucks.com/vboard/s...d.php?t=317684 Grams 53-1953 Chevrolet Belair http://67-72chevytrucks.com/vboard/s...=1#post4327784 1969 Chevy C10 Shortbed 4.5/6?" Frame off resto http://67-72chevytrucks.com/vboard/s...d.php?t=548136 1999 Toyota Tacoma 4x4

08-20-2009, 06:31 PM	#14
mclairmo Registered User Join Date: Jan 2006 Location: Take Off Posts: 1,908	Re: how to correctly use a vacuum guage.. Lower is full manifold vacuum. However, if the vacuum advance canister was hooked up to it, you may need to use a T so you can keep vacuum going to the vacuum advance canister while you tune the carb up with the vacuum guage installed.

08-20-2009, 07:27 PM	#15
cparman sharp as a marble Join Date: Jan 2007 Location: atlantic beach,florida Posts: 1,082	Re: how to correctly use a vacuum guage.. vacuum gauges can be a wonderful diagnostic tool if you let it. you can use it to adjust timing, by watching the gauge and turning the distributor until you have your highest vacuum reading. Sometimes you will have a gas ping, and will need to back off the timing a bit use it to know what power valve you need diagnose a burned valve make sure you have enough vacuum play with it, understand it, the gauge is a powerful tool

08-20-2009, 07:30 PM	#16
mclairmo Registered User Join Date: Jan 2006 Location: Take Off Posts: 1,908	Re: how to correctly use a vacuum guage.. "Luke, my son . . . may the vacuum force be with you."

08-20-2009, 08:31 PM	#17
oldblue1968chevy Grandpa in the rustmobile... Join Date: Nov 2008 Location: Spokane WA/Viola TN Posts: 11,422	Re: how to correctly use a vacuum guage.. Ok i'll try to play with the vacumn guage this weekend (gotta fix my wheeler first, so i can sell it to buy more stuff for the truck so i want the most vacum reading on the guage as I can...without pinging GOTCHA any more replys??... __________________ John Goose-1968 C10 355,9.32-1CR, Vortec Heads ,262 voodoo, 3.73:1 3OTT (HS ride/beater/farm truck) http://67-72chevytrucks.com/vboard/s...d.php?t=317684 Grams 53-1953 Chevrolet Belair http://67-72chevytrucks.com/vboard/s...=1#post4327784 1969 Chevy C10 Shortbed 4.5/6?" Frame off resto http://67-72chevytrucks.com/vboard/s...d.php?t=548136 1999 Toyota Tacoma 4x4



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08-20-2009, 10:50 PM	#18
TonyJohnson Registered User Join Date: Mar 2003 Location: Cheboygan, MI Posts: 998	Re: how to correctly use a vacuum guage.. When you're driving, they are also a good idicator of potential gas mileage. If you're running a lot of vacuum, your mileage will suck... __________________ Tony Johnson -- '71 Blazer w/L-31 Vortec 350, SM465, NP205, performer intake, edelbrock 1406, HEI, 4" lift, Boyd EFI tank, Vintage A/C My Blazer --

08-20-2009, 11:11 PM	#19
CG BlahBlahBlah Join Date: Feb 2002 Location: Wa. Posts: 19,992	Re: how to correctly use a vacuum guage.. Here's one I have, I got it off the 72 C10 Burb I gave to my son. Attached Images

08-21-2009, 06:02 AM	#20
'68OrangeSunshine Senior Member Join Date: Feb 2002 Location: Tucson, AZ USA Posts: 7,441	Re: how to correctly use a vacuum guage.. This subject came up last year in a thread titled: _Vacuum Cluster_ by Its70 on 4/03/2008. Sorry I don't know how to link threads. Anyway I use a vacuum gauge [Mooneyes 2-1/8"] in the dash of my daily driver. It tells me a lot about my engine's internal condition while moving. I have another hand-held Vac gauge in my tune up kit and we use it for tweaking up the carb. It's a great instrument, once you get the hang of it. __________________ Every 25 years I like to rebuild that 292, whether it needs it or not.

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