[72NovaGuy]

I finally decided to buy a vacuum gauge for helping tune the carbs a bit, Edelbrock 750s, on my 6-71 blown SBC. I was going off the vacuum/boost gauge in the car, but it was a pain to make an a adjustment and then walk back to the drivers window to see the reading.

Anyway...I found that when I hooked up the vacuum gauge to a manifold source on the carb it was 4" higher (14" reading) than the gauge in the car (10"). Should I be selecting my step up springs based off of the gauge at the carb fitting or the gauge in the car? The gauge in the car is hooked up to a fitting installed on the back of the blower manifold.

 

[allend43]

I'd be tempted to try a couple more vacuum gauges, till you figure out which one is correct first.

 

[bluedawg3t57]

Maybe try hooking the second gauge up to were the in car gauge is plumbed in.

 

[72NovaGuy]

Maybe try hooking the second gauge up to were the in car gauge is plumbed in.

I was thinking about doing that, it's just such a pain to get the damn fitting disoconnected back there. Not much room to work with my not so slender hands.

If I get the same reading at the fitting in the manifold as I was getting on manifold port on the carb with the vacuum gauge I just picked up yesterday should I just assume the Autometer gauge is incorrect?

Since I had been tuning the carb solely based off the gauge in the car for a couple years now I had switched out the 8" step up springs out of the carb that the previous owner had put in and I put in the 5" step up spring since I was only reading 6" of vacuum in gear while idling.

 

[forcd02]

I would use the reading off the carb, below the throttle plates-the manifold is below the rotors, so it might be diff
as long as the gauge is accurate
hook them both up in the same location, they prob would read the same

 

[72NovaGuy]

I would use the reading off the carb, below the throttle plates-the manifold is below the rotors, so it might be diff
as long as the gauge is accurate
hook them both up in the same location, they prob would read the same

That's what I was kind of thinking yesterday that if I'm reading 14" at the carb that is what the carb is seeing and I should base my step up spring selection based off the carb reading.

I'm still going to try and get the reading off the blower manifold port to check the accuracy of the gauge in the car as well.