1967 327/350 holley questions

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  • Duke W.
    Beyond Control Poster
    • January 1, 1993
    • 15491

    #16
    Re: 1967 327/350 holley questions

    ...or check the plug heat range to ensure that it is equivalent to AC heat range "5".

    The PO didn't know what he was doing and the OP is new to the vintage Corvette game, so he needs to do some simple ignition system checks before moving on to the carb.

    That's what I'd do, but after dealing with sixties vintage small blocks for 50 years what do I know.

    In the last few months I analyzed two '65s - a 365 and 350 HP. The 365 HP spark advance map was OE, and I don't recommend changing it other than bumping total WOT advance to the 38-40 degree range if it will tolerate that level without detonation. We did a complete blueprint/overhaul on the 350 HP distributor and remapped the spark advance with a different VAC and centrifugal springs as documented in the December thread.

    Both engines appeared to have the correct OE cams based on idle manifold vacuum readings, and both have the correct OE carburetor, which is the same for both engines.

    I found that the 350 HP engine idled best with the idle mixture screws out one turn from the seat, which is the initial recommended setting in the '65 Corvette Shop Manual Supplement idle/speed mixture adjustment proceedure, but the 365 HP idled best at 1.5 turns out, which makes sense. The higher overlap 30-30 cam yields much higher exhaust gas dilution at idle than the L-79 cam, so the 365 HP engine needs a richer idle mixture.

    I always start with simple things first - verify that the plugs are the correct heat range based on what we long term users have found works best - NOT what's in the owner's manual or a spark plug catalog, verify that the spark advance map is somewhere in a reasonable ballpark, and go through the idle speed/mixture adjustment procedure.

    If the above doesn't yield good performance and driveability without fouling plugs, then you have to dig deeper.

    Duke
    Last edited by Duke W.; January 28, 2013, 12:34 PM.

    Comment

    • Joe C.
      Expired
      • September 1, 1999
      • 4598

      #17
      Re: 1967 327/350 holley questions

      Originally posted by Duke Williams (22045)
      ...or check the plug heat range to ensure that it is equivalent to AC heat range "5".

      The PO didn't know what he was doing and the OP is new to the vintage Corvette game, so he needs to do some simple ignition system checks before moving on to the carb.

      That's what I'd do, but after dealing with sixties vintage small blocks for 50 years what do I know.

      Duke
      Multi Spark Discharge makes the system very forgiving of spark plug heat range. The original ignition is not. Furthermore, the symptoms as described in post #1 rule out ignition and definitely point to rich mixture.

      You make a critical assumption that the MSD was installed AFTER the plug fouling presented! Are you sure that this is the case?

      Comment

      • Joe C.
        Expired
        • September 1, 1999
        • 4598

        #18
        Re: 1967 327/350 holley questions

        Originally posted by William Ford (50517)
        Lots about this in previous threads. I agree I would suspect Holley. May be a bad power valve or some form of internal Holley gas leak or possibly high float level or pin hole in a float.. . If adjusting idle mixture screws have no effect on idle-it's a bad power valve or internal fuel leak. Unless you're restoring for judging, no need to remove MSD. I'll get some argument, but unless you like fooling with points, MSD distributor is solid and you can readily adjust advance curve. Assume it has vac advance as well as centrifugal. Have you checked initial and total timing with a dial back light?

        '67 L79

        '67 L36
        '62 340 hp
        All true............

        Comment

        • William F.
          Extremely Frequent Poster
          • June 10, 2009
          • 1354

          #19
          Re: 1967 327/350 holley questions

          Amen, Joe!

          Comment

          • Joe C.
            Expired
            • September 1, 1999
            • 4598

            #20
            Re: 1967 327/350 holley questions

            Originally posted by William Ford (50517)
            Amen, Joe!
            The OP has gone quiet.
            Somebody must have contacted him offline.
            Can you guess who?

            Comment

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