Are my vacuum readings correct?

[wazzabie]

I have a 78 K5 with federal emisions -350 chevy

here are my rpms settings

fast idle - 1600 rpms
idle rpm - 700 rpms

my vacuum at fast idle is 20
my vacuum at low idle is 13

Are my vacuum settings correct?\

Also timming is at 8 btc

 

[bot0611]

Shouldnt iddle read a higher vacuum?

 

[wazzabie]

Also I did not disconnect the hose to the vacuum advance when I took the readings or adjusted the idle mixture screws.

 

[bot0611]

AFAIK you dont need to, you disconnect it when you are setting timing.

 

[imiceman44]

Also I did not disconnect the hose to the vacuum advance when I took the readings or adjusted the idle mixture screws.

Yeah it's weird that you have higher vacuum at 1600 than at Idle, but you have decent vacuum at idle.

 

[ryoken]

I have a 78 K5 with federal emisions -350 chevy

here are my rpms settings

fast idle - 1600 rpms
idle rpm - 700 rpms

my vacuum at fast idle is 20
my vacuum at low idle is 13

Are my vacuum settings correct?\

Also timming is at 8 btc

I do have to ask this....

you do have it hooked up below the throttle plate correct? not a ported source on the carb?

 

[wazzabie]

I had it hooked up to the vacuum that goes out to the termal sensor that opperates the air duct in the intake.

Anyways I moved it to so now it sources from the vacuum for the tranny modulator.

The new readings at low idle are 14. It is not quite at 15. Maybe 14.5 at times. Is this ok?

Also at low idle the rpms can change bu as much asa 25 rpms up or down. Is this ok?

 

[wazzabie]

I do have to ask this....

you do have it hooked up below the throttle plate correct? not a ported source on the carb?

How can I tell if I'm connected to a ported source on the carb?

 

[ryoken]

a ported source is any port above the throttle plate...

 

[wazzabie]

My first connection was to a port source. Was that bad?

 

[ryoken]

thats why your readings where reversed... a ported source reads the opposite of manifold vacuum...

 

[Amtek]

Connect it anywhere on the intake manifold or on the base plate for the carb for accurate readings. A timed port will be above the carburator throttle plates, dont use them. Its not bad, but it wont give you correct vacuum readings.

 

[bot0611]

Theres the problem...

 

[imiceman44]

thats why your readings where reversed... a ported source reads the opposite of manifold vacuum...

I just realized the other post came after these responses, it explains the reversed readings.
I thought these numbers were after he connected to the tranny vacuum source.

 

[ryoken]

I always have to remind myself that the things oldschool gearheads like us take for granted, may not be as obvious to someone starting out...