Where to hook up vac lines on new carb

[Mrturner1]

So I just got a new Holley 650 double pumper and it's almost 100% installed. I'm hooking up all the vacuum lines and noticed I don't have a spot to plug the vacuum line that comes out of the valve cover into my carb. The big port on the back is being used by my th400 shift module, and I have the vacuum advance in the distributor hooked up to the small port under the throttle blades in front of the carb. I don't have power brakes or anything else to hook up, but the PCV from the valve cover has nowhere to go now. It's the same size as the transmission shift modulator so I can't use one of the small ports. Is it OK to put a T on the back so the shift modulator and PCV share the big back port?

It's my first Holley so correct me if I'm wrong on the vacuum advance being plugged in UNDER the throttle blades on the front of the carb too please.

Thanks for any help

Matt

[DANTIP]

Look at the documentation that came with your carb. It should show you where to hook up the valve-cover/pcv hose. Secondly, most "experts" suggest using manifold vacuum (under the blades) for distributor advance rather than "ported" vacuum. There are a few good explanations available on the internet.

Good Luck

[72 Super]

What type of intake are you running? Does it have s threaded port in the rear where you can add a vaccum port? On my 72 I have a 350 with a 750 Holley doubler pumper with a Victor Jr. Intake which does not have a location to use a Vaccum fitting. So I used an 1inch spacer user my carb wth a vacuum port. I have my PVC going to the port at te rear of the carb, my PB hose is going to the port on the carb spacer and my turbo 350 modulator vaccum is hooked to small port on passenger side of the carb. I know this is a little different than your set up, just giving you an idea.

Ray

[Mrturner1]

Can I just do it this way with a T hooked up to the big port on the back of the carb? I have an Edelbrock performer RPM and it does have the large vacuum port on the back and that's where my transmission line used to go but the Holley carb is in the way of that now. I do have my back and advance hooked up to manifold vacuum under the throttle blades, so Is it OK to have the PCV and the transmission modulator both running to a T off the back of the carb?

[Mrturner1]

Don't mind my spark plug wire mess Lol

[the idiocracy]

Originally Posted by Mrturner1

So I just got a new Holley 650 double pumper and it's almost 100% installed. I'm hooking up all the vacuum lines and noticed I don't have a spot to plug the vacuum line that comes out of the valve cover into my carb. The big port on the back is being used by my th400 shift module, and I have the vacuum advance in the distributor hooked up to the small port under the throttle blades in front of the carb. I don't have power brakes or anything else to hook up, but the PCV from the valve cover has nowhere to go now. It's the same size as the transmission shift modulator so I can't use one of the small ports. Is it OK to put a T on the back so the shift modulator and PCV share the big back port?

It's my first Holley so correct me if I'm wrong on the vacuum advance being plugged in UNDER the throttle blades on the front of the carb too please.

Thanks for any help

Matt

You don't want to tie the PCV to the shift modulator, you run the risk getting oil from the PVC line in there. I would put a breather on the pcv valve and call it a day.

For the vacuum advance line, you want to grab ported vacuum. I am not sure about the port under the throttle blade, I know that on the Holley there should be a 10-32 set screw above the air bleed screw on the primary metering block. I found an extended set screw and drilled it for a vacuum fitting. if you run manifold vacuum to the advance, it will work, but part throttle driveability and fuel mileage suffers a little.

[72 Super]

Originally Posted by Mrturner1

Can I just do it this way with a T hooked up to the big port on the back of the carb? I have an Edelbrock performer RPM and it does have the large vacuum port on the back and that's where my transmission line used to go but the Holley carb is in the way of that now. I do have my back and advance hooked up to manifold vacuum under the throttle blades, so Is it OK to have the PCV and the transmission modulator both running to a T off the back of the carb?

Just so you know, they make a low profile vaccum port fitting for the Performer RPM Intake. It is
Elderbrock 8096 it's available from summit, kegs, Amazon etc. You can search it to see a picture and infomation on it.

Ray

[72 Super]

Originally Posted by Mrturner1

Can I just do it this way with a T hooked up to the big port on the back of the carb? I have an Edelbrock performer RPM and it does have the large vacuum port on the back and that's where my transmission line used to go but the Holley carb is in the way of that now. I do have my back and advance hooked up to manifold vacuum under the throttle blades, so Is it OK to have the PCV and the transmission modulator both running to a T off the back of the carb?

Just so you know, they make a low profile vaccum port fitting for the Performer RPM Intake. It is Elderbrock part # 8096. You can search it to see a picture and infomation. It is available through Jegs, summit, Amazon etc.

Ray

[Mrturner1]

Originally Posted by the idiocracy

You don't want to tie the PCV to the shift modulator, you run the risk getting oil from the PVC line in there. I would put a breather on the pcv valve and call it a day.

For the vacuum advance line, you want to grab ported vacuum. I am not sure about the port under the throttle blade, I know that on the Holley there should be a 10-32 set screw above the air bleed screw on the primary metering block. I found an extended set screw and drilled it for a vacuum fitting. if you run manifold vacuum to the advance, it will work, but part throttle driveability and fuel mileage suffers a little.

What is the advantage of having the PCV hooked to the carb? Seems like oil would pass through (tiny bits obviously) like you were saying, so wouldn't it be bad? What happens if I just have a breather on both valve covers instead of a PCV?

[69chevytrucker]

the one on the valve cover should go into the air cleaner port

[Mrturner1]

Originally Posted by 69chevytrucker

the one on the valve cover should go into the air cleaner port

My air cleaner has a port forgot to plug into, you're sure that's where it goes? Because it was plugged into the carburetor when I bought it

[69chevytrucker]

Originally Posted by Mrturner1

My air cleaner has a port forgot to plug into, you're sure that's where it goes? Because it was plugged into the carburetor when I bought it

yes it is there so the vapor mixes with the air again and goes through the carb again.

[69chevytrucker]

the one on the back of the intake goes to the brake booster the one big one on the carb goes to the trans the one little one the right of the carb goes to the dizzy the other little one is usually capped off

[69chevytrucker]

the little capped off one is sometimes used for vac accessorizes like vac cruze control or with some cars vac headlights etc

[geezer#99]

You guys got it all backwards!
Well, some of you do!
The big port on the carb is for the pcv from one valve cover.
The other valve cover has a breather on it. Either a stand alone one or hooked to the air cleaner. You need air into the motor to mix with the fumes and drawn out by the pcv.
No pcv and two breathers makes for a crankcase pressure problem and possible oil leaks.
Vac modulator wants manifold vac. Either a manifold port on the carb or hooked to a vacuum tree on the intake.
The manifold vac port and the ported port are for your vac advance. Run which ever one your motor likes. Usually a big cam motor needs manifold vac. Stockish motors run on either one.

[70STOVEBOLT]

Are you running an air cleaner spacer? If so, it has a large hose nipple that will run to one of your valve covers. The other valve cover will have the pcv valve, which should be hooked to the big port on the back of the carb. The transmission modulator should be hooked to the intake manifold port behind the carb (use the low profile fitting mentioned above), or it can be hooked to the small port below the throttle blades, but that will only leave you with ported vacuum for your vacuum advance. Like geezer said, if the engine has a healthy cam, it will want manifold vacuum.

[GASoline71]

If you run that rubber line down to the the vac modulator on the trans, it will collapse and not give you correct shift points. It's whay there is a hard line running down there from the factory.



I also used the stock manifold port for my modulator line. I ground out a bit of the top of it to clear my Holley 3310 before I put a spacer underneath it. EZPZ fix.

Gary