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Using an original ignition coil on my '67

Discussion in '1965-1970 Shelby Mustang GT350 & GT500' started by skidado, Aug 4, 2007.

  1. Aug 4, 2007 #1
    skidado

    skidado Well-Known Member

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    I have recently had my motor refreshed and have put a few hundred miles on it to break it in. I have started using a bit more throttle (occational wide-open throttle up to 4000 rpm), and I am dissapointed with the performance of the engine.

    I'm not expecting much, since it is stock spec motor, and I am running all standard ignition system (no fancy electronics). ('67 GT350 #02751)

    My problem is this. Not only is the engine a little 'soft', but it is sooting the plugs and smells strongly like it's running rich. I have set the float levels to factory spec (as advised here on this forum last summer), I have done the valve lash, points gap and plug gaps all to stock spec, and set the ignition timing, but still it runs rich.

    On occation, it drops a couple of cylinders (usually during warm-up).

    I have replaced all the parts of the ignition system, except the coil. It is the original factory-fitted piece, and I was wondering if the performance of a coil could deteriorate over time, such that the spark at the plugs becomes too small to burn all the gas in the combustion chamber, thereby losing power and pushing un-burnt fuel into the exhaust system. I have only ever know coils to stop working altogether and suddenly.

    I will try another coil on the car, but does it sound plausible that a forty year old coil could slowly deteriorate and cause these kinds of symptoms?

    Any advice from the Knowledge Collective would be much appreciated.

    Thanks

    David
     
    skidado, Aug 4, 2007
    skidado, Aug 4, 2007
    #1
  2. Aug 4, 2007 #2
    OVERRIDE

    OVERRIDE Well-Known Member

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    It could be the power valve in your carb that is bad and making it rich. If you turn your idle mixture screws in one at a time if the engine does not die the pawer valve is bad.

    Mike
     
    OVERRIDE, Aug 4, 2007
    OVERRIDE, Aug 4, 2007
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  3. Aug 5, 2007 #3
    Texas Swede

    Texas Swede Well-Known Member

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    Hi,
    I am pretty sure your problem is in the carb. Two summers ago I had this problem on my 67 and it was the secondary float level and the needle
    didn't close so there was fuel leaking down into the engine which made it
    run very rich. Friends driving behind me said it was a black cloud of smoke
    when I accelerated. I replaced the complete secondary float bowl with
    the correct float level adjustment and a healthy needle and the problem went away.
    Texas Swede
     
    Texas Swede, Aug 5, 2007
    Texas Swede, Aug 5, 2007
    #3
  4. Aug 5, 2007 #4
    skidado

    skidado Well-Known Member

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    Thanks for these replies. I have run some resistance tests on the coil and it is giving roughly the right readings. I tried turning the idle screws in one at a time and the engine didn't die.

    So it sounds like the carb. Does anyone know where I can get a rebuild kit with the correct power valve and float needles for my original shelby carb?

    Many thanks

    David
     
    skidado, Aug 5, 2007
    skidado, Aug 5, 2007
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  5. Aug 5, 2007 #5
    OVERRIDE

    OVERRIDE Well-Known Member

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    Hi David

    You need a new power valve. If the engine Did die when you turned the screws in then the power valve is good. But your valve is bad. When you replace the power valve make sure you get the right one for your carb.
    Your old should have 2 numbers on it.

    Mike
     
    OVERRIDE, Aug 5, 2007
    OVERRIDE, Aug 5, 2007
    #5
  6. Aug 5, 2007 #6
    rr64

    rr64 Well-Known Member

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    Holley Power Valve Warning

    It's not worth much perhaps but what I bought as Holley brand new power valves in the last couple of years have been inconsistent in quality. I spent a lot of time chasing a power valve problem in a 1967 GT500 more than 32 years ago so ever since I test them to make sure they will seal off. I was working on a 1969 Boss 302 carburetor not long ago and the brand new valve closed crooked. As vacuum pulled the valve shut the stem skewed off to one side and would never seal. I was working on a 427 Cobra carburetor and the valve closed but the machining was so rough on the cone and seat it would never seal off. These days I buy two or three extra even if the kits have valves in them and keep only the ones that seal off correctly.
     
    rr64, Aug 5, 2007
    rr64, Aug 5, 2007
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  7. Aug 5, 2007 #7
    r.dilabio

    r.dilabio Member

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    Hello skidado! the best source for carb.stuff here in the colonies is most likely jon enyeart @ pony carbs.in new mexico.they are well stocked and could mail you whatever you require.I would really suggest you do an oil change if you have been running rich for any lenght of time.It will keep your new engine from wearing out,as fuel contaminated oil is not a good lubricant..let us know if you need more info/help.
     
    r.dilabio, Aug 5, 2007
    r.dilabio, Aug 5, 2007
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  8. Aug 6, 2007 #8
    skidado

    skidado Well-Known Member

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    This is why I love this forum! Thanks for all the replies. I will certainly look at the new valve to make sure it seals properly.

    Also, the oil change - Yes! I thought this might be a problem, so I checked the oil, and it smells of gas! Time to change.

    I see Branda does a Holley rebuild kit specifically for the 715cfm carb - I might as well do a complete clean-and-rebuild job while I'm at it!

    Thanks again

    David
     
    skidado, Aug 6, 2007
    skidado, Aug 6, 2007
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  9. Aug 6, 2007 #9
    1175

    1175 Well-Known Member

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    If you need a new set of floats, I have a few extra NOS sets.
     
    1175, Aug 6, 2007
    1175, Aug 6, 2007
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  10. Aug 7, 2007 #10
    skidado

    skidado Well-Known Member

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    I pulled the power valve out last night, and it has no numbers or letters on it at all. If I recall correctly, I installed it back in about 1987 from a Jiffy kit.

    I couldn't tell how well it is seating because the seat is hidden inside the sealed assembly. However, the stem looks a little 'wonky' :thumbdown

    I've ordered the full rebuild kit for the 715 CFM Holley from Branda.

    David
     
    skidado, Aug 7, 2007
    skidado, Aug 7, 2007
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  11. Aug 7, 2007 #11
    Texas Swede

    Texas Swede Well-Known Member

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    Hi David,
    Please be aware that I haven't seen any kit they
    sell today for Holley 3259, 3259-1, that includes
    the correct power valve. It should be #85 that opens
    at 8.5 inches of mercury. You have to buy that one
    separately. Original Holley number is 25R-239A-85.
    I think Holley uses a new part number for it now but
    I haven't found it. I bought a new some time ago at
    Autozone. If you can't find it, send me a personal
    email and I'll see if I can find one and send it to you.
    Texas Swede
     
    Texas Swede, Aug 7, 2007
    Texas Swede, Aug 7, 2007
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  12. Aug 7, 2007 #12
    AJD350

    AJD350 Active Member

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    While you have the carb apart, check the front carb body surface for flatness with a straight edge. I spent some time chasing an inconsistent carb. Hard starting, long crank times, part throttle surge. If the body is warped, the metering block gasket will not seal around the accel pump transfer port (right above the power valve well). Raw fuel will dribble into the well and vacuum will draw it into the intake. You can have it machined flat, or carefully file the surface flat, as I did. Thoroughly clean out the passages after. Night and day difference on my car! Good luck on your problem.

    Al
     
    AJD350, Aug 7, 2007
    AJD350, Aug 7, 2007
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