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Thread: Rough Run -1968 PU

  1. #1
    Join Date
    Feb 2009
    Posts
    3

    Default Rough Run -1968 PU

    My 304 runs rough when choked or when cold. I have checked the spark plygs and I have a Pertronix ignition... any ideas?

  2. #2
    Join Date
    Feb 2009
    Posts
    19

    Default

    Hi,

    It sounds like you need to check your air fuel mixture. Does it run rough when warm?

    KB-14

  3. #3
    Join Date
    Feb 2009
    Location
    Aiken, SC
    Posts
    2,423

    Default

    A rough running engine when cold means that the fuel is not atomizing enough. That's a symptom of cold air and cold gas in a cold engine. That's why idle speed when cold is higher than idle speed when hot. Faster moving air mixes with gas better.

    Your cold idle should be about 12-1500 rpms. Warm engine, about 625-650. I use 625 for an automatic, 675 for a manual.

    The choke on a 68 should be manual. There is also a hand throttle. You will learn how to finesse it so that it runs when cold, and how to lower the idle as it warms up.

    The less advance you have, the better your cold starts and cold idle will be. The 68 uses ported vacuum from the carb on the vacuum advance.

    With the engine warmed up:

    Set the timing at about 4 degrees BTDC with the vacuum advance disconnected and the vacuum line plugged. Set the idle at 650 or so, highest possible vacuum. You'll have to keep trading off adjustments, idle mix, timing, idle mix, timing...

    Unplug the vacuum line. Got vacuum? Not good. There should be no vacuum from the carb until you give it some throttle. Blown power valve, possibly.

    Nevermind. Hook it back up. It should still run okay if your vac advance diaphram isn't defective. Get back to us and tell us what happened, and we'll tweak it from there.
    Allan E.
    Curmudgeon Extraordinaire
    Charter Member, Old Hippie IH Club
    Old fashioned binder freak

  4. #4
    Join Date
    May 2010
    Location
    Houston, TX
    Posts
    208

    Default Another old post revisited.

    Quote Originally Posted by Allan E. View Post
    A rough running engine when cold means that the fuel is not atomizing enough. That's a symptom of cold air and cold gas in a cold engine. That's why idle speed when cold is higher than idle speed when hot. Faster moving air mixes with gas better.

    Your cold idle should be about 12-1500 rpms. Warm engine, about 625-650. I use 625 for an automatic, 675 for a manual.

    The choke on a 68 should be manual. There is also a hand throttle. You will learn how to finesse it so that it runs when cold, and how to lower the idle as it warms up.

    The less advance you have, the better your cold starts and cold idle will be. The 68 uses ported vacuum from the carb on the vacuum advance.

    With the engine warmed up:

    Set the timing at about 4 degrees BTDC with the vacuum advance disconnected and the vacuum line plugged. Set the idle at 650 or so, highest possible vacuum. You'll have to keep trading off adjustments, idle mix, timing, idle mix, timing...

    Unplug the vacuum line. Got vacuum? Not good. There should be no vacuum from the carb until you give it some throttle. Blown power valve, possibly.

    Nevermind. Hook it back up. It should still run okay if your vac advance diaphram isn't defective. Get back to us and tell us what happened, and we'll tweak it from there.
    I have a 1962 Scout 80 with a Holley 1904 on top of my 152.
    If my Vaccum Advance line comes directly from the Carb do I have a "Ported" Vacuum? FYI: It seems several alterations have been made to the overall Vacuum system by PO's. The wipers are now electric and I can't find any other vacuum lines under the hood.

  5. #5
    Join Date
    Feb 2009
    Location
    Aiken, SC
    Posts
    2,423

    Default

    Quote Originally Posted by radar232 View Post
    I have a 1962 Scout 80 with a Holley 1904 on top of my 152.
    If my Vaccum Advance line comes directly from the Carb do I have a "Ported" Vacuum? FYI: It seems several alterations have been made to the overall Vacuum system by PO's. The wipers are now electric and I can't find any other vacuum lines under the hood.
    From the carb is ported vacuum IF it's not present at idle. The power valve is supposed to kick in after you move the gas pedal. If it works, leave it alone.

    Yes, your scout has been modified, probably by somebody who knew what they were doing.
    Allan E.
    Curmudgeon Extraordinaire
    Charter Member, Old Hippie IH Club
    Old fashioned binder freak

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