how to correctly use a vacuum guage..

[oldblue1968chevy]

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]

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

[Jacfourteen]

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?

[Jacfourteen]

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)

[oldblue1968chevy]

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

[Jacfourteen]

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]

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]

ok

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

[mclairmo]

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]

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]

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.

[68gmsee]

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.

[oldblue1968chevy]

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]

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]

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]

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

[oldblue1968chevy]

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]

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]

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

['68OrangeSunshine]

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.