Vacuum Gauge

[Jono.B]

Hi All,

 

recently I was given a vacuum gauge and I was jusrt wondering what a vaccum gauge actually tells you. I hooked it up to the line from my vaccum advance on the dizzy that runs to the carb. the vacuum seems to build up when accelerationg until the second butterfly opens it then goes down. is the vaccum just pressure building up between the time of the fiirst opening and the secondary opening??

[parrot]

Connect the vacuum line from the guage to a take off on your inlet manifold.

 

It gives you an indication of economy.

 

i.e. you put your foot down and the needle swings to poor, cruising along needle is on good.

[Jono.B]

ok, any ideas of which part?? ie the tube from the manifold to rocker cover???.

 

 

must say it looks cool hooked up to the vacuum advance hose coz of how it goes up then when i floor it it goes down real fast like non existent boost :jamie:

[styler]

a vacuum gauge tells you lots of things if you know how to read it right,

there are some articles on the net about it if you have a look.

[Jono.B]

So could someone please tell me the correct hose to Tee the connector into, photos would be helpful, I don't know which vacuum hose to use. I have the aisin twincarbs.

 

thanks again all,

 

Jono.

[Super Jamie]

Anywhere on the intake manifold.

[towe001]

Anywhere on the intake manifold.

After the carby or throttle body. Basically what your after is "ported vacuum"

Eg - Tee it in to the vacuum hose that runs from the carby to the dizzy

 

Or as a last resort the hose that runs to the brake booster - But if there's is a one way valve in the line have your tee piece between that and the manifold

 

http://www.international-auto.com/index.cfm?fa=ad&aid=48

http://autospeed.com/cms/A_2393/article.html

[Jono.B]

well currently I have it on the line from the carb to the Dizzy but when Idling it reads as zero then when I accelerate slowly it goes up to like 20 then when I floor the pedal or give it a bit more gas the needle goes back down to zero so it looks like some kind of anti-boost. So I think I need to find a different spot. how about the hose from the rocker cober to the manifold??

[styler]

its more difficult with with twin carbs as far as i know, you need connect the 4 carb intake runners

to a common line and run a pressure damper to get a decent reading, we discussed it on toymods,

do a search there.

[Jono.B]

I don't even have 4 carb intake runners I think. I have the hose from the PCV valve to the manifold. the vaccum advance from the main carb to the dizzy (second carb doesnt have one) and the hose from the brake booster to the manifold, also there is a large fitting on the left side of the intake manifold but I never connected rthat to anything.

[Taz_Rx]

Just run dual vacuum guages! :dance:

[towe001]

well currently I have it on the line from the carb to the Dizzy but when Idling it reads as zero then when I accelerate slowly it goes up to like 20 then when I floor the pedal or give it a bit more gas the needle goes back down to zero so it looks like some kind of anti-boost.

Idling at zero doesn't sound right it, should be up more around 20. Sounds like you have the timing way off its mark and maybe other things

In a way your right with calling it "anti-boost" cause when the needle drop to zero the motor is seeing no pressure at all expect for normal air pressure. But it shouldn't be dropping all the way to zero anything above and between zero and 5 is ok

I don't even have 4 carb intake runners I think. I have the hose from the PCV valve to the manifold.

I wouldn't do that. You'd be running pressurized fumes from the motor.

the vaccum advance from the main carb to the dizzy (second carb doesnt have one) and the hose from the brake booster to the manifold, also there is a large fitting on the left side of the intake manifold but I never connected rthat to anything.

You have it connected to right hose

 

 

Note - all thins is being taken from a single carb and not a twin carb. But either way i can't see there being anything different. The other carby should have a vacuum connection in the same spot as the "main' carby it'll just have it blocked off - try swapping the gauge over and see if there's any difference in readings. Both readings should be pretty close together

[Jono.B]

****Note - all thins is being taken from a single carb and not a twin carb. But either way i can't see there being anything different. The other carby should have a vacuum connection in the same spot as the "main' carby it'll just have it blocked off - try swapping the gauge over and see if there's any difference in readings. Both readings should be pretty close together*****

 

the second carb does not have the vacuum connection in the same place..

 

The vaccum connection on the carb I am using is the one down the bottom of the carb however both carbs have a little vaccum connector at the top just below the airl filters.. should I be using that part. ??