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Breather Cap Question

Discussion in 'Engine & Performance' started by Moose Drool, Feb 28, 2021.

  1. Raider L

    Raider L Full Access Member

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    That was the very first thing I did as soon as I got my truck home. I ripped all the smog crap off and threw it all away! All these pipes that screwed into the top of each of the exhaust manifold port places on each bank. And all the hoses that went to all that and that went to the smog pump. I found some straight thread brass plugs to put in each one of those holes in the exhaust manifolds. I blocked off the EGR valve, more EPA crap, and threw the EGR valve in the trash! The PCV valve I kept. It has a function that's important. Anything other than the carb and the headers, not including the PCV, dist., etc., is unecessary. Rip it off your engine and get rid of it. Any gases your truck is emitting don't change the damn weather or cause starving in Africa! It's all nothing but government telling you what you have to have to drive down the road!
     
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  2. idahovette

    idahovette Full Access Member

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    Don't have a clue, do ya?
     
  3. Bextreme04

    Bextreme04 Full Access Member

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    That sure escalated quickly....
     
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  4. just_some_guy

    just_some_guy Supporting Member Supporting Member

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    Glad I came across this thread and I apologize for the hijack, but I have a similar situation going on here, I believe.

    My 350 has nothing on the drivers side valve cover. The passenger side valve cover has an oil fill/breather cap on the front, and this bent metal piece coming out of the rear that literally hooks to nothing. I am having a valve seal job done next week and I have a new set of valve covers to put on there as well as a new intake manifold. Please pardon the mess under the hood. I just got this thing less than 2 months ago and am in the process of trying to sort through all the stuff the PO did to it. Anyway, do I need to hook this thing into the carb? Sorry for the noob questions here but I am not too familiar with these older carbureted motors (or motors in general LOL).

    Thanks for any advice. I again apologize for the thread hijack.

    [​IMG]
     
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  5. Octane

    Octane Full Access Member

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    No.You can remove and plug it as long as you have the breather cap on the valve cover.That pipe hooked to a crankcase air filter mounted on the inside of the factory breather.You need a pcv on the driver side cover with it hooked to the vac. port on carb tho.
     
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  6. just_some_guy

    just_some_guy Supporting Member Supporting Member

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    Thank you! Appreciate the advice. I'll let them know when I take it in for the valve seal job.
     
  7. 75gmck25

    75gmck25 Full Access Member

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    Lets clear up some confusion - all crankcases need ventilation to reduce blow-by and prevent oil leaks, and GM started using it long before the PCV valve.

    In early SBCs (and other vehicles) they used a draft tube system, where the crankcase had a vent tube that extended down to near the bottom of the engine on the outside. As you drove along, the air rushing by the tube under the vehicle created a vacuum and pulled air out of the crankcase to reduce pressure.

    Sometime later, GM and other manufacturers decided to implement a "positive" crankcase ventilation system and they started using the PCV valve.
    - In the passenger side valve cover there is usually a tube leading up to the air cleaner and a small filter, or there is a filtered breather cap in the valve cover. This is where the fresh air is drawn in.
    - In the driver's side valve cover there is usually a PCV valve. The PCV valve is connected to the base of the carburetor by a 3/8" rubber hose. Whenever you run the vehicle you will get vacuum drawing on the PCV valve, which allows air to be pulled out of the crankcase and into the intake. As the carburetor pulls air out, the breather cap in the other valve cover is letting fresh air in. The PCV valve is designed to be closed under high vacuum (idle, etc.) when blow-by is low, and open under high load/ low vacuum, when blow-by is high.

    Bruce
     
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  8. Octane

    Octane Full Access Member

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    Some of our semi truck engines still have a pipe hooked to valve cover and run down to the bottom of engine for crankcase venting.A little oil and vapors are always coming out of the pipe.On my personal road tractor that vapor and oil mix is probably related partly to the 1.3 million miles on my engine.
     
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  9. Goldie Driver

    Goldie Driver Full Access Member

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    What would the second vacuum source be needed for on an auto tranny ?

    All I can think of offhand is the modulator.

    Curious- thanks !
     
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  10. Turbo4whl

    Turbo4whl Supporting Member Supporting Member

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    Vacuum Tip-in switch for the locking convertor.
     
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  11. Goldie Driver

    Goldie Driver Full Access Member

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    Aha ! I gots one of those, too.

    :D

    Thanks!
     
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  12. Moose Drool

    Moose Drool Member

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    I finally had the time to plumb the PCV. It started right up after sitting for a week. The idle skyrocketed to 1300. It never idled that high. What would a good idle be to set it at?
     
  13. Bextreme04

    Bextreme04 Full Access Member

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    That should be the correct range for cold start high idle. To adjust your idles and idle mixtures I would start at a cold start.

    Turn your idle mixture screws in until they lightly bottom out and then pull out two full turns.
    Warm the truck fully by driving it around for about 10 miles or so.
    Disconnect the vacuum advance from the distributor, block the wheels, and set the parking brake before putting it in drive and letting it idle for the rest of the mixture adjustment.
    Set your idle to 700rpm using the idle adjustment screw on the DRIVER side of the carb.
    Slowly turn out ONE idle adjustment screw until the rpm peaks.
    Reset rpm to 700.
    Turn in THE SAME idle screw until rpm drops to 600-650rpm(depending how lean you want your idle mixture).
    Repeat the idle mixture adjustment for the other idle mixture screw.
    Now plug in the vacuum advance on the distributor and set the idle RPM to your desired RPM(I prefer 650-700).
    Put the truck back in park and check the idle rpm in park to make sure you find it acceptable. \


    Then let it fully cool and do the high idle adjustment on a cold start. One pump of the pedal all the way to the floor and slowly let up to make sure the choke is set and on the high idle cam.
    Start the truck and let it idle for a few minutes until the rpm has built all the way up onto the cam(this should start at around 750-800rpm and build up to around 1200rpm)
    Turn the high idle adjustment screw on the PASSENGER side of the carb(its small and behind the choke housing usually).
     

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