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Old 09-17-2015, 02:15 PM   #1
edwardgonzalez
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Rochester vacuum port help

I recently purchased a 305 from a junkyard. It's a great engine it's clean but it also came with a lot of emission items that I have no need of. My truck has nothing for emissions so I took everything off. The carburetor that was on the engine was computer-controlled. I have a spare Rockchester carburetor so I threw that on the intake. I'm not sure what to do with all of the vacuum ports hopefully you guys can help me out. The The only vacuum items that I know for sure that I have are the vacuum advance to the carburetor, PCV valve ,and there is a vacuum hose going to my transmission. What can I Cap off and what else is needed. I know that the booster is vacuum controlled but that goes in the big hole in the back right? I was planning on capping the egr valve. Also there was another port coming out of the intake next to the thermostat housing with two hoses coming out of it. What is that for and can I It off or plug it? Thanks guys
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Old 09-17-2015, 02:16 PM   #2
edwardgonzalez
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Re: Rochester vacuum port help

Sorry here is a picture of the back
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Old 09-17-2015, 02:39 PM   #3
Dead Parrot
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Re: Rochester vacuum port help

#6 Power Brake booster.
#3 PVC valve.
#4 probably output to charcoal canister.
#5 is normally about where the vacuum advance hooks in. Might be #1 on this one. If skipping emissions, connect your vacuum advance to manifold vacuum.
#2 no clue.
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Old 09-17-2015, 04:20 PM   #4
edwardgonzalez
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Re: Rochester vacuum port help

Here's the first picture again
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Old 09-18-2015, 10:56 AM   #5
VonDog
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Re: Rochester vacuum port help

On mine, I capped #1,2,4. #5 goes to vacuum advance and the bigger rear does go to the brake booster. #3 to PCV. What year carb is it? There are a lot of variations of the quadrajets and the year will help sort things out. The serial number will give you the year. It's on the left side of the carb stamped vertically an a flat spot. This one is off an 85 Cadillac.
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