50 hp merc.

Discussion in 'Bubba's Outboards' started by drpepper, Apr 22, 2008.

  1. drpepper

    drpepper New Member

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    Ok... '78, 4cyl., 50 hp merc. elec. start-- no spark, not even a weak one from the #3 & 4 coils.

    ~ goin' through it, It obviously needed a stator, so I put a new one on it, even though it ohm'ed out good, it had corroded bare wires (the two yellow/red stripe wires going to the rectifier.)

    I swapped coils/plugs and plugwires around and still no fire from the coils 3 & 4..... Not the coils.

    The trigger ohm'ed out good but has a bare/corroded wire (the wht/blk stripe wire to the switch box) and is on order.
    but since it checked good, I taped it up to continue the diag

    put the new stator on... still no fire 3 & 4 ( as I expected since the old stator tested ok.)

    checked all wires from coils to switchbox and grounds--- good shape.

    whats left? the switchbox? I understand the only method is trying a new one... see if it fixes the problem, but will a switch box cause only two out of four coils to crap-out? Anyway, I have one on order.

    what are all other possible causes of these two coils not firing besides the coils, plugs/plug wires, stator, trigger and switchbox?

    Even though the trigger ohm'ed out good, could it still somehow be the culprit or not?

    even though I've tried to be clear about the fact I'm fighting an electrical problem with no spark from two of the coils themselfs, I probably need to mention that the compression is 122psi EXACTLY on ALL 4 cylinders (very good)

    I appreciate ANY input, Thankyou.
     
  2. Bubbakat

    Bubbakat New Member

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    There is no known test for a switchbox but by process of elimination which you have done. Yes a a switch box can cause loss of spark on two cylinders. If that stator ohmned good and all else did also the the switch box is most time at fault.
     

  3. drpepper

    drpepper New Member

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    6,133
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    Thank you bubba... so I can feel better about forkin' over the 300+ bucks for that lil sucker... anyway, I guess the right way is to replace ALL ignition system components at the same time when they have alittle age on 'em. I am a driveability tech at a Ford dealership and that helps although a 2 stroke outboard is a little different animal then what I'm used to. I'm certain when I get fire on those two coils, I'll have more questions *because* the 42 dollar book I bought ain't worth much of a crap.
    Is the any other "things" common to these engines or suggestions that you know of to warn me about BEFORE I get this thing out on the Ohio river with the BOC members in June?
    Thanks again, Bill
     
  4. Bubbakat

    Bubbakat New Member

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    Yep the air and fuel mix at the carb is real teadeous and I'll post the proper procedure for doing that this evening. It will fasll on its face when you try to accelerate if not set right. It takes two people to set one. You need to set the screws while someone else operates the boat because it needs to be done while in gear under a load.
     
  5. drpepper

    drpepper New Member

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    Bubba, I think your psychic! I've already noticed Those carbs dribbling fuel... I sure am glad you're around! Thank you! I promise I'll do my homework first and try hard not to pester you with a million questions... Thanks again~ Bill
     
  6. drpepper

    drpepper New Member

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    6,133
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    Since I made the post above I went and picked-up my switch box and installed it.... I got fire!!! ( I know this because I pulled the plug-wire while it was runnin' and it shocked the shit out of me) I'm still waiting on the trigger and it won't be here for a week but I'm gonna replace the water pump-- take it down to the river, and follow your instructions for adjusting the carbs... I'm feeling alot better about things now!~ Bill
     
  7. Bubbakat

    Bubbakat New Member

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    AWH the old shock treatment will let you know every time.:smile2: