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Edelbrock/Carter Idle Settings after PCV fitment

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    Edelbrock/Carter Idle Settings after PCV fitment

    After some very sensible advice from members I've fitted a previously absent PCV (positive crankcase vacuum) to my 64 289, using an Edelbrock valve cover cap piped to the PCV vacuum port on the front of my Edelbrock/Carter 4 barrel carb. Got the cap at very reasonable price from John Woolfe Racing in the UK. No more whisps of smoke/fumes from the valve cover cap But the engine idle speed has risen markedly since doing the job. Would be grateful for any explanation - and advice on rectifying this please. Thanks guys

    #2
    This increase in idle speed is to be expected. The PCV system has introduced a measured air leak to the manifold to enable fumes from the crank case to be sucked into, and burnt by the engine. You really need to readjust the idle settings which is quite simple. You need to adjust the throttle stop screw where the throttle linkage joins the carb and the two mixture screws sticking out of the front of the carb. First run the engine until it is fully warmed up. A trip around the block would be best. Then unscrew the throttle stop screw until the engine idle speed returns to normal. With this done slowly screw either one of the mixture screws clockwise (noting the fractions of a turn) until the engine starts to go lumpy then screw it anticlockwise 1/2 turn. Do the same with the other mixture screw turning it the same amount as the first screw. If the engine starts to go lumpy as soon as you start turning the mixture screws try unscrewing them anticlockwise. What you are looking for is the smoothest idle you can get. The other way to do this is with a vacuum gauge fitted to the engine where you are looking to get the highest vacuum possible at idle but I am assuming you don't have one of these. My suggestions will get you the smoothest idle with the engine running as lean as you can for lowest emissions at idle.
    Allan

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      #3
      Originally posted by ALLAN R View Post
      This increase in idle speed is to be expected. The PCV system has introduced a measured air leak to the manifold to enable fumes from the crank case to be sucked into, and burnt by the engine. You really need to readjust the idle settings which is quite simple. You need to adjust the throttle stop screw where the throttle linkage joins the carb and the two mixture screws sticking out of the front of the carb. First run the engine until it is fully warmed up. A trip around the block would be best. Then unscrew the throttle stop screw until the engine idle speed returns to normal. With this done slowly screw either one of the mixture screws clockwise (noting the fractions of a turn) until the engine starts to go lumpy then screw it anticlockwise 1/2 turn. Do the same with the other mixture screw turning it the same amount as the first screw. If the engine starts to go lumpy as soon as you start turning the mixture screws try unscrewing them anticlockwise. What you are looking for is the smoothest idle you can get. The other way to do this is with a vacuum gauge fitted to the engine where you are looking to get the highest vacuum possible at idle but I am assuming you don't have one of these. My suggestions will get you the smoothest idle with the engine running as lean as you can for lowest emissions at idle.
      Thanks Allan - makes perfect sense. I did back off the throttle stop screw completely and it still ran fast - so I'm guessing the idle mixture is WAY too rich ?? Will adjusting those mixture screws do the job or is there something else going on here ?

      Comment


        #4
        Ok just to see where those mixture screws are set screw them fully clockwise until they bottom out counting the turns. A good starting point is for them to be around 1 1/2 turns out. If they are a lot more out than this then this could be your trouble. They should also be set about the same. Start with this and see if you can get the engine to idle at a sensible speed. It does sound as if the engine is running rich. Another issue could be that the secondary throttle plates are being held a little too far open but I can't remember what the throttle stop arrangement is for these, you need to look around the carb. Don't fiddle with this until you have tried adjusting the mixture screws.

        I found this, scroll down to Figure 8 where you need to check that the secondary's are closing properly. Someone before you may have been fiddling with the carb.

        https://static.summitracing.com/glob...rbsrebuild.pdf
        Allan

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          #5
          I always find a video is useful to work out what to do with anything and there are a couple of useful Edelbrock carb tuning videos that I watched before first stripping down and then setting up my 4 barrel carburettor..



          Comment


            #6
            Thanks muchly fellas - will have a go at this as soon as I can !

            Comment


              #7
              Allan, from reading your posts I think you have only one component of a PCV system the cap with a vent tube. This should be connected to the air cleaner, You also need a PCV valve this is usually fitted with a grommet in the other valve cover, a pipe connects this to the vacuum port on your carburettor. Watch this video it explains the system well especially the operation of the valve at the end of the video. https://youtu.be/DTlCep4_jZA


              Comment


                #8
                Originally posted by Martin XJ View Post
                Allan, from reading your posts I think you have only one component of a PCV system the cap with a vent tube. This should be connected to the air cleaner, You also need a PCV valve this is usually fitted with a grommet in the other valve cover, a pipe connects this to the vacuum port on your carburettor. Watch this video it explains the system well especially the operation of the valve at the end of the video. https://youtu.be/DTlCep4_jZA

                Thanks Martin - a very informative video and it does appear that I've got half a system. Does anyone know where I get a PCV valve and valve cover grommet pls ?
                Thanks to Allan I've successfully adjusted the idle mixture. It was set far too rich as suspected

                Comment


                  #9
                  Iikaleica apologies for calling you Allan, got you mixed up with ALLAN R. You should be able to get a valve and grommet from any of the Mustang parts dealers. Be careful where you drill the hole for the grommet, it needs to be between two pairs of rockers so there is no interference. Hope this makes sense. Martin.
                  .


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                    #10
                    The cap you bought should have the PCV valve within it. Just to make absolutely sure pull the cap out of the rocker box and the bottom of it should have a sort of piston assembly that you can push up against a light spring. The filler cap just has metal gauze in it.
                    Allan

                    Comment


                      #11
                      Originally posted by ALLAN R View Post
                      The cap you bought should have the PCV valve within it. Just to make absolutely sure pull the cap out of the rocker box and the bottom of it should have a sort of piston assembly that you can push up against a light spring. The filler cap just has metal gauze in it.
                      Hi Allan - must have bought the wrong cap because mine has no piston or spring assembly (though it has no holes on the underside with gauze) just a take-off elbow. However I can use that cap on the opposite valve cover and pipe it to the air cleaner. I've ordered a bung and PCV valve for the other valve cover to connect to the base of the carb and that should be job done hopefully ! It seems plenty of people don't bother with the link to the air cleaner from the second valve cover but certainly on later cars that was how it was rigged. As always there 's more than one way to skin a cat !

                      Comment


                        #12
                        Thats a shame with the cap because the advert did say PCV. I bought a pair of alloy rocker covers that have a pair of caps of identical size and shape but one is the filler cap and one is the PCV. As for the pipe from the filler to the air cleaner the USA did go through a phase of connecting the breather pipe to the air cleaner to ensure the engine burnt its own fumes, but the PCV system supersedes that system as it keeps the engine crank case below atmospheric pressure so no fumes should escape. No harm in connecting it up if you have or want to put a fitting in the air cleaner.
                        Allan

                        Comment


                          #13
                          Originally posted by ALLAN R View Post
                          Thats a shame with the cap because the advert did say PCV. I bought a pair of alloy rocker covers that have a pair of caps of identical size and shape but one is the filler cap and one is the PCV. As for the pipe from the filler to the air cleaner the USA did go through a phase of connecting the breather pipe to the air cleaner to ensure the engine burnt its own fumes, but the PCV system supersedes that system as it keeps the engine crank case below atmospheric pressure so no fumes should escape. No harm in connecting it up if you have or want to put a fitting in the air cleaner.
                          Thanks again Allan - as you say, the Edelbrock description did suggest the PCV was built in. I'm grateful for the explanation of the system because when I removed the Edelbrock air cleaner yesterday I realised there is no port for a pipe connection anyway - and I was scratching my head. So I won't bother with any air cleaner connection and just rely on the push-in PCV from Customville to connect from the right hand valve cover to the front of the carb

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