Thread: Building A looper Beast

  1. #521
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    Quote Originally Posted by Fastjeff57 View Post
    Very interested in your ignition system. I'm running an old Mark 78 using the later Merc electronic distributor. Have several of those switch boxes 'hanging around' and would love to utilize them to fire my 'baby six'.

    Seeing this is an alternator driven, high voltage input system, can I ask how you generate that voltage (with a stock type stator, I suppose) and how you are timing it?

    Thanks,

    Jeff
    The stator has both batt charge windings and coils for charging the ignition system

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    Team Member R Austin's Avatar
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    The last of the in line 6 Mercs ran the same ignition as the V-6. It is not a drop in for the belt driven CDI systems as the block is cut a 1/16 shorter on the top end cap surface. As stated, the flywheel and stator winding's produce both battery charging and ignition charging outputs. The trigger is in the center of the stator windings and locked in the full advanced position by the link rod on the left side just under the flywheel. Timing is set with the old fashion timing light with degree marks laid out on the flywheel.
    The CDI system is more than enough for the Mark engines. It is what we ran on the alcohol burning 6's back in the day. There are plenty of those parts floating around. The only difference in the green switch boxes was the tach sender signal, 4 vs 6. Not using tach signal, run either box.

  3. #523
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    Thanks. Good Keeper File info.

    I run one of those belt drive CDI systems on my Mark 78, but I must disagree with you that parts are plentiful. Getting hard to find a good used distributor (trigger) for these.

    Jeff
    "We live at the bottom of an ocean of air." - General Marvage Slatington

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    Team Member R Austin's Avatar
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    Quote Originally Posted by Fastjeff57 View Post
    Thanks. Good Keeper File info.

    I run one of those belt drive CDI systems on my Mark 78, but I must disagree with you that parts are plentiful. Getting hard to find a good used distributor (trigger) for these.

    Jeff
    The only part that may be a problem is the trigger if you are using the first version that had a bolt in replaceable unit. The later units used a potted tower section. Three different lengths. 3, 4 & 6 cylinder, pick your length and use 6 cylinder chopper wheel. RePair did rebuild those triggers.

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    I'm currently using a 4 cylinder unit with the 6 cylinder chopper wheel. It works fine, but I'd love to get a spare distributor in case....you know. Getting hard to find. CDI sells one, but for nearly 400 bucks!

    As a Winter Project I'm going to convert the stock, dual points Mark 78 distributor to electronic using HEI modules from GM cars. One module will work half the cylinders, the other one the rest, with two high performance coils. Should be interesting!

    Jeff
    "We live at the bottom of an ocean of air." - General Marvage Slatington

  6. #526
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    Quote Originally Posted by Fastjeff57 View Post
    I'm currently using a 4 cylinder unit with the 6 cylinder chopper wheel. It works fine, but I'd love to get a spare distributor in case....you know. Getting hard to find. CDI sells one, but for nearly 400 bucks!

    As a Winter Project I'm going to convert the stock, dual points Mark 78 distributor to electronic using HEI modules from GM cars. One module will work half the cylinders, the other one the rest, with two high performance coils. Should be interesting!

    Jeff
    Hope that works for ya, those Hei units fall of at about 6000, that's 3000 in two stroke terms.

  7. #527
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    With one HEI running 3 cylinders, and the other running the rest, I should easily get 6,000 rpms (think 6 cylinder 4 stroke at 6,000 rpm). Motor tops out before that in any case.

    Jeff
    "We live at the bottom of an ocean of air." - General Marvage Slatington

  8. #528
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    [QUOTE=Fastjeff57;152634]With one HEI running 3 cylinders, and the other running the rest, I should easily get 6,000 rpms (think 6 cylinder 4 stroke at 6,000 rpm). Motor tops out before that in any case.
    Jeff[/

    It isn't how many cylinders as much as it is the processor in the module being able to keep up. At 6 grand on a four cycle is where these things fell off. That is 3 grand on a two stroke as it fires every time not every other like a four stroke. Mad makes some better modules though but not good enough for 10 grand,

  9. #529
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    Your math is off: Three cylinders (2 stoke) at 6 grand equals 6 cylinders (4 stroke) at 6 grand. I plan to use two HEI modules, each firing 3 cylinders. Got it?

    Jeff
    "We live at the bottom of an ocean of air." - General Marvage Slatington

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    Quote Originally Posted by Fastjeff57 View Post
    I'm currently using a 4 cylinder unit with the 6 cylinder chopper wheel. It works fine, but I'd love to get a spare distributor in case....you know. Getting hard to find. CDI sells one, but for nearly 400 bucks!

    As a Winter Project I'm going to convert the stock, dual points Mark 78 distributor to electronic using HEI modules from GM cars. One module will work half the cylinders, the other one the rest, with two high performance coils. Should be interesting!

    Jeff
    Operative words " It works fine" . With all due respect, the Merc battery CDI is all any 6 cylinder Mark series deflector will ever need. Anything else is a waste of money. Distributor bodies can found on E Bay most any time.

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