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  1. #1

    Default 4-112 won't run for more than an hour

    Late fifties(?) model starts up easily, runs smoothly for just about exactly an hour, and then starts to misfire (according to mechanics, it is not technically "misfiring", so i will call it "hiccuping".). The engine will be running, it feels smooth, exhaust sounds great, and then I will feel the engine hiccup and at the same time, I'll hear a single, slightly different burbly note from the dry exhaust. It will run fine for a few minutes and then hiccup again. The frequency of these hiccups increases gradually until it is simply running rough and the exhaust is an irregular burble and sputter. It will stall at the one hour mark, +-10 min.


    If i let it sit for 20 min, the engine will start up again and run for about 15 min before eventually stalling the same way.


    Engine temperature never goes above 170.
    Oil pressure around 20.
    Coil (and when it had one, the external ballast resistor) very hot, but according to infrared thermometer, within spec.
    Engine was possibly/probably originally running on 6v system.


    What has been tried so far:


    Mounted external ballast resistor on aluminum bracket for improved cooling. No improvement.


    Fuel was originally gravity-fed. Installed fuel pump, regulator and gauge, fuel return line and also removed fan that was apparently meant to cool the coil. Tried several different coils, some with external, others internal resistors. Replaced Pertronics Ignitor, all spark plug leads, plugs. Swapped back over to points ignition (which was found on boat, along with at least four coils, two resistors and a tangle of spark plug leads. These items, along with the fan aiming cooler air at the coil in the engine compartment, suggest to me someone has been chasing down an electrical solution to the engine's poor performance...). Put Pertronics back in, and engine ran worse than ever.


    Just installed brand new updraft carburetor. Engine ran great for 30 min, then started it's usual decline ending in a stall at the one hour mark.


    Side note, but it might be useful:
    Just installed 100w solar panel with charge controller. Lights were indicating it was charging normally when I had the engine running (poorly) at low rpms. Thought I'd see if it would change at higher revs, of course it didn't, but soon noticed the solar charger control panel had gone dark and would not come back to life.


    Help wanted! Thanks.

  2. #2
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    Default Re: 4-112 won't run for more than an hour

    Coil could be getting too hot. IF you're running a 6v coil on 12v, that a failure waiting to happen. If the coil gets too hot, the top pops off and oil comes out. I did that once 4 wheeling with A WWII jeep. You also could be getting vapor lock. Gas in the lines gets so hot it boils, creating air pockets. The increased pressure can push fuel back thru the pump. Usually solved by installing an electric fuel pump. In the 1950s, people use to put tin foil around their fuel line, between the pump and carb, to act as cooling fins.

  3. #3

    Default Re: 4-112 won't run for more than an hour

    Definitely 12v coil
    Electric fuel pump installed

  4. #4
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    Default Re: 4-112 won't run for more than an hour

    I'd suggest some more investigating before more parts changing occurs.

    you need to determine if your hiccup is due to fuel issues or ignition issues.

    have you checked the rest of secondary side of the ignition-cap & rotor? is the hiccup associated to a single cylinder or multiple cylinders?

    Another possibility, suggested by the nominal one hour run time, is the fuel tank had crud in it that may be accumulating on the screen on the pickup tube (or in the anti-syphon valve)...a vacuum gauge on the suction side of the pump will help here....

  5. #5

    Default Re: 4-112 won't run for more than an hour

    New info:
    Problem is definitely spark!
    (Installed inline spark testers which showed good, steady spark on all cylinders until it starts to fail, then irregular spark first on aftmost cylinder, then all cylinders until failure. Tried to start it immediately, no spark)


    Makomark, what is and how do I check "the rest of secondary side of the ignition-cap & rotor"?


    Mechanic has checked timing but only on properly-running engine, not at or near failure. An old-timer has suggested advancing the timing a tiny bit because...I don't understand why. Thoughts
    ?

  6. #6
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    Default Re: 4-112 won't run for more than an hour

    with your update, I'd would guess that rest the secondary side of the ignition is ok and your issue is either the coil (failing as it heats up) or on the primary side.

    I'd think I'd go thru the pertronix installation sheet to make sure everything necessary was done. if that's ok, I'd put the spark tester on the coil lead and use a volt meter on the coil and then run it again.....again, initial guess is either the petronix unit is quitting or the coil is quitting...…

    could also be bad wire/connection on the primary side....or maybe the tach is starting to go - you can disconnect its wire at the coil ….

    Another potential is that the distributor is worn out mechanically...would have hoped your mechanic would have already done a thorough inspection there...

  7. #7

    Default Re: 4-112 won't run for more than an hour

    Pertronics installed correctly, good ground.
    Installed new plugs (d-16s) and leads (carbon core) just for fun.
    Disconnected tach.

    Ran engine for an hour, then it started to fail. Had testers on 3 of 4 cylinders and this time it very much looked like spark was intermittent on only one of them. Curiously this was the same cylinder that melted the boot of the spark tester...

    Whole time coil receiving 13.85v, generator putting out 15.75v

    https://youtu.be/CZCQ1e4Tacc

    Next will put tester on coil wire, what should I test with voltmeter?
    How do I check for worn distributor?

  8. #8
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    Default Re: 4-112 won't run for more than an hour

    Sound like the regulator on the generator is a bit high....

    Also, if the 13.85VDC is on the '+' side of the coil, was that with the ballast resistor installed?

    do you know is the resistor is matched for the coil?

    which pertronix module are you using?

    If the wear is bad enough, you can feel the shaft rocking in the bearing when you push it back and forth, parallel to the breaker plate. the best way is to have it checked on a old style distributor machine....

  9. #9
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    Default Re: 4-112 won't run for more than an hour

    one of the pertronix sheets in my library suggests you may need two ballast resistors in series on a 4 cylinder....this is the same concern with the 'is the resistor matched to the coil?' question above...

  10. #10

    Default Re: 4-112 won't run for more than an hour

    Yeah, thought generator reading a bit high. Will see if adjustable.

    Yes, 13.85v is on positive side of internally resisted coil. No ballast resistor required.

    Using original PerTronix (black and red wire)

    Definitely some movement in distributor, but if I remember correctly, one of the mechanics declared it good enough.

  11. #11
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    Default Re: 4-112 won't run for more than an hour

    understand on the coil...

    I doubt the pertronix unit was original....to you, yes, but not when the engine was made.

    the rotor will have ~ 10 deg of rotation (due to the advance mechanism) but should not move side to side ....radial play...

  12. #12

    Default Re: 4-112 won't run for more than an hour

    meant original pertronix (pertronix 1, as opposed to P ii, or P iii)

    will check distributor for play

  13. #13
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    Default Re: 4-112 won't run for more than an hour

    understand on 'original'; re the pertronix unit.

    after re-reading the whole thread, two additional thoughts come to mind..

    First, there's a significant voltage drop in your ignition feed circuitry....suggested maybe a corroded connection that slowly heats up - if the +13.8VDC reading is consistent at the coil's + terminal, then this isn't likely a factor. that said, the drop between battery and the coil (with an internal resistor) should be less than 0.5VDC.

    The other thing is fuel starvation due to crud in the tank that accumulates on the pickup tube as the engine is run....engine shuts off and gravity will slowly let the crud drop so 'seeing the culprit' directly can be a challenge. a vacuum gauge on the suction line, at the fuel pump inlet, is a preferred diagnostic there.

    Anyhow, just food for thought...

  14. #14

    Default Re: 4-112 won't run for more than an hour

    Edit:
    Generator generating 14.75v (not 15.75)

  15. #15

    Default Re: 4-112 won't run for more than an hour

    This from PerTronix Support
    If the unit works fine when the motor is cold and then goes bad as it heats up, it is a ground issue. test the ground at the distributor itself. Most common error is the clip that holds the distributor down is painted or corroded. Take it off and make sure there is a clean surface. We also see in many situations where the ground wire from the battery to the motor in a boat is bad or corroded.

    Does this mean that the distributor has a separate ground (apart from the PerTronix ground)?


  16. #16
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    Default Re: 4-112 won't run for more than an hour

    Sounds to me that they are saying most people just use the hold down clip to 'ground the distributor' and this is far from ideal....adding a dedicated ground wire would be a good idea.

  17. #17

    Default Re: 4-112 won't run for more than an hour

    Dedicated ground wire is installed. Less than 0.2 ohms resistance from mounting plate to battery (green wire to engine ground)
    We don't know what happens when it's running.
    Click image for larger version. 

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    Last edited by BlackDuck; Yesterday at 09:08 PM.

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