Another PCV Question
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Melting Slicks
Joined: Dec 1999
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From: Pensacola FLA
Another PCV Question
I currently have a new 4160 Holley on my rebuilt 65 327/350hp. Since the carb does not have the vacuum orifice elbow like the 2818 carburetor, does it require the use of a pcv valve between the oil fill tube and the vacuum port on the front of the carb?
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Usually the pcv screws right into the oil fill tube, the opening faces to the fuel pump side at an angle backwards, and if I remember right the carb vent was on the back on my 4160holley (66 300hp),connected to the pcv with rubber hose.
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Last edited by Kerrmudgeon; Jan 27, 2010 at 06:29 PM.
Thread Starter
Melting Slicks
Joined: Dec 1999
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From: Pensacola FLA
What would happen if I took the pcv valve out of the system?
Drifting
Joined: Dec 2002
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From: Long Beach CA
The answer to your question is...that depends. My '65 327-300 had a road draft tube coming out of the back of the block. If you still have that, you don't need a PCV valve. If you don't, you need some way to vent the crankcase. The standard system is a PCV valve hooked to the vacuum side of the carb or the intake manifold, and a breather tube going into the air cleaner. Just a PCV valve without a breather is not effective.
Thread Starter
Melting Slicks
Joined: Dec 1999
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From: Pensacola FLA
The answer to your question is...that depends. My '65 327-300 had a road draft tube coming out of the back of the block. If you still have that, you don't need a PCV valve. If you don't, you need some way to vent the crankcase. The standard system is a PCV valve hooked to the vacuum side of the carb or the intake manifold, and a breather tube going into the air cleaner. Just a PCV valve without a breather is not effective.
Another question I have about the pcv valve is....Can the pcv valve cause an idle surge?
Burning Brakes
Joined: Jun 2000
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If you're gonna use a 1966/67 design PCV valve instead of the original 1965 design brass carb elbow (.090" orifice), then yes, it should have the correct PCV valve (CV790C or equivelent) inserted in the proper direction (vacuum side -vs- pressure side) between the front fill tube and full manifold vacuum source (anything below the throttle plates), which it looks like yours currently is. I also see you have the proper 65 air cleaner breather tube already installed.
You need to fix your distributor vacuum advance hose and plumb it into full manifold vacuum as well, not carb ported as you have it now.
...and yes, an incorrect / wrongly installed / inoperable PCV valve can cause an idle surge due to it becoming a vacuum leak. But I'd fix your vacuum advance hose first.
You need to fix your distributor vacuum advance hose and plumb it into full manifold vacuum as well, not carb ported as you have it now.
...and yes, an incorrect / wrongly installed / inoperable PCV valve can cause an idle surge due to it becoming a vacuum leak. But I'd fix your vacuum advance hose first.
Last edited by Viking427; Jan 28, 2010 at 09:34 AM.
Team Owner
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From: Washington Michigan
How old is that carb, and what's the LIST number on the front of the choke air horn? Most later generic Holley 4160's have a large (3/8") nipple in the baseplate for the PCV hose connection just forward of the right rear attaching stud hole.
Thread Starter
Melting Slicks
Joined: Dec 1999
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From: Pensacola FLA
If you're gonna use a 1966/67 design PCV valve instead of the original 1965 design brass carb elbow (.090" orifice), then yes, it should have the correct PCV valve (CV790C or equivelent) inserted in the proper direction (vacuum side -vs- pressure side) between the front fill tube and full manifold vacuum source (anything below the throttle plates), which it looks like yours currently is. I also see you have the proper 65 air cleaner breather tube already installed.
You need to fix your distributor vacuum advance hose and plumb it into full manifold vacuum as well, not carb ported as you have it now.
...and yes, an incorrect / wrongly installed / inoperable PCV valve can cause an idle surge due to it becoming a vacuum leak. But I'd fix your vacuum advance hose first.
You need to fix your distributor vacuum advance hose and plumb it into full manifold vacuum as well, not carb ported as you have it now.
...and yes, an incorrect / wrongly installed / inoperable PCV valve can cause an idle surge due to it becoming a vacuum leak. But I'd fix your vacuum advance hose first.
Full manifold vacuum on the distributor? I thought it supposed to be carb ported. There is small vacuum inlet tube at the front base of the carb next to where I have the the pcv hose connected for full manifold vacuum. That's where I hooked up my vacuum gauge to set the idle mixture screws. What benefits would result in going to full time vacuum? Any drawbacks?
I purchased the carb last year from OReillys. Here are the numbers off the air horn 80457-8 and 2579. The carb has a front vacuum inlet tube that looks like it's 3/8" in size and a 3/8" inlet tube at the back of the carb. It has a carb ported inlet tube on the passenger side above the idle mixture screw and a small inlet tube next to the front 3/8" inlet tube.
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Burning Brakes
Joined: Jun 2000
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..yes, trust us on this, or peruse the 100's of archived threads on this subject. Benefit is steady, unfluctuating vacuum at idle, no drawbacks.
Thread Starter
Melting Slicks
Joined: Dec 1999
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From: Pensacola FLA
..yes it should, assuming the OEM design brass elbows were seeing full manifold vacuum as well, this I don't know. The 65 elbows were located about 1/2 way up on Holley carb bodies, so it could have been ported or less than manifold vacuum that high up. Someone more familiar wiith 65's carbs will need to weigh in on that.
..yes, trust us on this, or peruse the 100's of archived threads on this subject. Benefit is steady, unfluctuating vacuum at idle, no drawbacks.
..yes, trust us on this, or peruse the 100's of archived threads on this subject. Benefit is steady, unfluctuating vacuum at idle, no drawbacks.
Team Owner
Joined: Oct 2000
Posts: 38,897
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From: Washington Michigan
..yes it should, assuming the OEM design brass elbows were seeing full manifold vacuum as well, this I don't know. The 65 elbows were located about 1/2 way up on Holley carb bodies, so it could have been ported or less than manifold vacuum that high up. Someone more familiar wiith 65's carbs will need to weigh in on that.
The vacuum connection for the PCV elbow fitting with the .090" orifice in it on the driver's side of the original Holley 2818 used in '64-'65 was a full manifold vacuum source.
If the setup in the photo has the PCV valve hose connected to a 3/8" nipple in the baseplate, it should work fine. There should be a smaller nipple adjacent to it that's a full manifold vacuum source - that's where you want to connect the distributor vacuum line.
Thread Starter
Melting Slicks
Joined: Dec 1999
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From: Pensacola FLA
The vacuum connection for the PCV elbow fitting with the .090" orifice in it on the driver's side of the original Holley 2818 used in '64-'65 was a full manifold vacuum source.
If the setup in the photo has the PCV valve hose connected to a 3/8" nipple in the baseplate, it should work fine. There should be a smaller nipple adjacent to it that's a full manifold vacuum source - that's where you want to connect the distributor vacuum line.
If the setup in the photo has the PCV valve hose connected to a 3/8" nipple in the baseplate, it should work fine. There should be a smaller nipple adjacent to it that's a full manifold vacuum source - that's where you want to connect the distributor vacuum line.
