setting carb with vacuum gauge

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gotdust57@yahoo

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i am going to adjust my edlebrock 600 cfm carb with vacuum gauge and need to know which hoses to plug or unplug to get accurate reading? thanks
 
You need to plug into a full vacumn port to get the right reading.Make sure the timing is set correct and then turn the mixture screws in or out to get the highest reading on the guage,then turn them back in a 1/4 turn,mrmopartech
 
Your looking for a small hose fitting near the base of the carb or in the manifold itself. hoo the gauge up and start the car. If the vacuum needle suddenly drops toward zero when you open the throttle you've got the right port. If the needle moves slowly or goes up plug that one back up and find the one with an instantaneous needle response.
 
Reviving this from the crypt, as I bought a vacuum gauge and will be looking to tune Dads cuda. Im hoping to spend time effectively as I wont have a lot of time and wanna drive it asap.
Engine is 273 4bbl with an aftermarket Eddy 1405...we added a choke as an afterthought. Can anyone add to this?? Someone posted a link recently to a cool website on how to best use a vac gauge and I cant find it.

Thanks all!
 
Mopar to ya said:
Gotta try and tune mine. Holley 750dp has a large vacuum at the rear (firewall side) that I use, correct?
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Any port on the carb or the manifold that has full manifold vacuum. I disconnect my brake booster and hook up there.
 
Bad Sport said:
Any port on the carb or the manifold that has full manifold vacuum. I disconnect my brake booster and hook up there.
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Brake booster port on carb worked ok Bruce?? I have no idea, other than I read on another site to not use that port?? Just curious....


Edit...sorry Bruce just read on the site that Inertia posted to hook to PB port
 
I don't know why not, as long as it is full manifold vacuum. You do not want to use the timed port (for dizzy vacuum advance) as long as you get full manifold vacuum it should be fine.

I just re-tuned mine today.

You are talking about the port on the back of that Eddy?
 
Some brake booster ports may have check valves on/in them.

I would go off carb base or intake manifold vacuum port.
 
Bad Sport said:
I don't know why not, as long as it is full manifold vacuum. You do not want to use the timed port (for dizzy vacuum advance) as long as you get full manifold vacuum it should be fine.

I just re-tuned mine today.

You are talking about the port on the back of that Eddy?
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Yep, same carb you sold me n Pops. I just chkd the Eddy manual and it states to adjust with screws, but I would rather use the gauge.

So simply adjust each idle mix screws until max vac is reached without increasing idle rpm right?
 
Adjust each screw watching the gauge until it doesn't increase anymore, then back it off 1Hg. It may very well increase the idle, but you can adjust that up or down to where you want it, as long as it doesn't drop your vacuum reading.

When I did mine today I ended up with 15Hg and about 900 rpm on the idle, any lower and my vacuum dropped which messes with my brake booster. Since you have other than stock cam yours will probably be similar.
 
4spdragtop said:
Yep, same carb you sold me n Pops. I just chkd the Eddy manual and it states to adjust with screws, but I would rather use the gauge.

So simply adjust each idle mix screws until max vac is reached without increasing idle rpm right?
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If the screws are off even a little, idle speed WILL change. Max vacuum also pretty much = highest idle speed.

Make sure engine is COMPLETELY warm to normal temp, and that no vacuum accessories are unplugged. On original later cars this would mean AC controls, booster, smog devices (heated air filter) etc

If idle changes much as you adjust, "re" adjust idle speed screw to get idle speed "where you want." As you get both the speed and the mixture closer and closer to "where they should be" these changes will be less and less

TIMING must be adjusted FIRST, but an extreme example might be a new engine with unknown distributor and carb. "Everything" will be "off." So "rough in" timing, "rough in" mixture and speed, until you get it close enough to set timing

AFTER YOU GET TIMING set "you are happy," from that point leave timing alone.

Then finish up with vacuum / idle mixture and keep idle speed in check.
 
I always thought it was: warm it up and time it-turn idle screws to get highest vacuum, then reset idle speed, repeat with screws and then repeat with idle speed? Vacuum web site is very informative.
 
Thanks guys! Cant wait to get home and start tweakin'!
To be honest Bruce, Dad n I bolted it on, broke in cam, adjusted idle and thats about it. As much as I wanted to "tinker" then...I didnt know what I was doing....not that I do now, maybe just enough to make me dangerous...LOL
 
Timing first. Especially initial/idle timing.

Timing affects carb settings. Not the other way around.
 
Anything at the Carb throttle blades,of below is manifold vacuum,as is Bad Sport's intake runner reference
. Highest idle speed non smog ,works as well. Set the damn timing first. Cams need more initially, possibly up to 14-22. Thanks to Crackedback on timing,still Need to light mine back up.Ask questions,be patient. Ig takes days here,it took me years.
 
Abodybomber said:
Anything at the Carb throttle blades,of below is manifold vacuum,as is Bad Sport's intake runner reference
. Highest idle speed non smog ,works as well. Set the damn timing first. Cams need more initially, possibly up to 14-22. Thanks to Crackedback on timing,still Need to light mine back up.Ask questions,be patient. Ig takes days here,it took me years.
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Yep, back in the day me and a couple buddies, would tinker, fart and try just about anything...we werent always successful, but sometimes we were. Nowadays thanks to the net and FABO. You get experienced/qualified answers right away :blob:
 
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