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Flathead Ignition - Sanity Check My Setup Please

Discussion in 'The Hokey Ass Message Board' started by Psychobilly Boi, Sep 23, 2010.

  1. Hi Guys,

    I posted on a thread here
    http://www.jalopyjournal.com/forum/showthread.php?t=514265&page=2
    about some issues I have been having with my flathead. Its basically running rough, will not accelerate, backfires and generally will not make it up a hill in any gear.

    I'm guessing its either fuel or ignition so I have decided to check ignition first as I have a multimeter and parts are cheaper to replace then new Stromberg 97's. Its running a 12V negative ground system, with a two bolt 1942 crab dizzy.

    I have a couple of general questions about the setup - I just need a sanity check on my thinking.

    Coil wiring
    The coil has (+)ive feed from the ignition to the (+)ive terminal on the coil. The (-)ve terminal has a wire from there to the post on the crab dizzy (where the condensor attaches to) as well as a wire back to my tach. Is this correct?

    The terminal post on the crab dizzy
    Is this post meant to be insulated from the dizzy housing? I ask because I have been told it is mean to be isolated but in my case it isnt. Doing a continuity test with my mutimeter showed continuity between the brass post and the distributer housing. It was dark so I will make sure that either the ring terminal for the condensor or the (-)ve wire from the coil isnt touching the distrubuter body somewhere.

    Is there supposed to be any washers or insulators between the ring terminal for the condensor on the post and the (-)ve coil wire?

    Coil resistance
    I realised I've been using a coil designed to be used with a ballast resistor. I dont have one and from what I read this will give the coil 12V and not the ~7V it is designed for. I used a multimeter to test the primary and secondary windings on the current and an old coil with the following results:

    Manufacturer Specifications
    Primary: 1.1 Ohm
    SecondaryL 8k Ohm

    Coil In Car
    Primary: 0.6-1.6 Ohm
    Secondary: 15.4k Ohm

    These readings would be cause to suspect I've killed the coil and it should be replaced?

    I'm attacking the issue methodically I just want to make sure that my thinking hasnt gone haywire!

    Danny
     
  2. Bruce Lancaster
    Joined: Oct 9, 2001
    Posts: 21,682

    Bruce Lancaster
    Member Emeritus

    Post should be isolated but you need to check it with both points open OR with paper inseted to stymy their grounding instincts.
     
  3. Aquaroscoe
    Joined: Apr 13, 2006
    Posts: 315

    Aquaroscoe
    Member

    Here is how I thought it works

    For positive ground the "+" terminal goes to the distributor (to be grounded on the engine block). For negative ground the "-" terminal goes to the distributor (to be grounded on the engine block).

    http://mgaguru.com/mgtech/ignition/ig104.htm
     
  4. Hi Bruce,

    Once again you save my head from exploding. So the points in the system will close completing the path to ground as part of their operating cycle. Makes sense! I'll double check no issues by holding the points open as you say.

    Thanks again,

    Danny
     

  5. Brilliant! Cheers mate.
     

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