R12 ignition gremlins
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Thread: R12 ignition gremlins

  1. #1
    Fellow Frogger! IThompson's Avatar
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    Default R12 ignition gremlins

    I went for a drive on sunday and my r12 was misfiring.
    It progressively got worse and i limped home.
    It would idle ok and full throttle high revs were mostly ok otherwise it would miss and jump around as i drove.
    I also noticed that the ignition coil was very hot.

    On saturday I replaced the points and the condenser as the previous points had degraded within 6 months. I found the condenser had not been connected adequately. Bare wire twisted together and not soldered.
    I also did an oil change.


    I think that i should replace the distributor cap and rotor as they look warn. (Bosch). Is this likely to have been accelerated by the disconnected condenser?

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    Would it be recommended to replace the coil as well? I was a bit concerned that it was very hot.

    Point gap was set to 18 thou
    Timing 0deg tdc
    Fuel BP 98
    Spark plugs gap looks ok
    Spark plug colour grey.

    Any thoughts?

  2. #2
    1000+ Posts REN TIN TIN's Avatar
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    Missing at low revs but okay at idle and high revs is usually a sign of a dirty or blocked jet in the carby.
    i.e. the idle jet and secondary jet are clear but the main jet is fouled.
    (Am assuming this is a Weber 32DIR)
    You sure it's an ignition problem?

    Cheers
    Ren
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    1000+ Posts daffyduck's Avatar
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    0 degrees? Most motors come in 10-15 before TDC. I would double check that.

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    Fellow Frogger! IThompson's Avatar
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    Ren,

    I rebuilt the carby with new gaskets a month back.
    I have had blocked primary jet problems before and this felt different.

    I am guessing ignition issues because it started after i replaced the points and condenser. I looked at the tiny filter on the carby fuel inlet and it looked perfectly clean.

    I put a screw driver in the end of a sparkplug lead and held the shaft near the engine block and the spark seemed small.

    Ian

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    1000+ Posts daffyduck's Avatar
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    Narrow point gap doesn't give the coil time to reach full saturation. Wider gap will give hotter spark.

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    COL
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    Hi ian

    I have had the points close up, that is the rubbing block on the points wears down which will alter the dwell angle and also the timing. Resulting in similar symptoms as you describe.

    The condenser is there for the purpose of reducing the arc when the points open which helps preserve the mating faces of the points.

    I would just reset everything back to factory specs and if its running fine leave well alone.
    Regards Col

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    Fellow Frogger! IThompson's Avatar
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    Col,

    I was attempting to set it as per the book but it still ran poorly.

    The distributor is probably 40 years old .
    Is it likely the cap and rotor button need replacing?

    Isn

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    1000+ Posts driven's Avatar
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    Quote Originally Posted by daffyduck View Post
    Narrow point gap doesn't give the coil time to reach full saturation. Wider gap will give hotter spark.
    Dwell angle is the amount of time (measured in degrees of distributor cam rotation) that the contact points remain closed. Initial point gap determines dwell angle.

    If the points are set too wide they open gradually and dwell angle (the time they remain closed) is small. This wide gap causes excessive arcing at the points and, because of this, point burning.
    This small dwell doesn't give the coil sufficient time to build up maximum energy and so coil output decreases.

    If the points are set too close, the dwell is increased, but the points may bounce at higher speeds and the idle becomes rough making starting harder. The wider the point opening, the smaller the dwell. The smaller the gap, the larger the dwell.

    Adjusting the dwell by making the initial point gap setting with a feeler gauge is sufficient to get the car started but a finer adjustment should be made. A dwell meter is needed to check the adjustment.

  9. #9
    COL
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    Quote Originally Posted by IThompson View Post
    Col,

    I was attempting to set it as per the book but it still ran poorly.

    The distributor is probably 40 years old .
    Is it likely the cap and rotor button need replacing?

    Isn
    Hi Ian

    That 0 deg for the timing is just a starting point so that you are able to start the car and it will run. You will need to advance the timing more, either using a timing light or by road test. I usually do a road test by accelerating in top gear from 50 KPH to about 70 KPH and listening for pinging. Keep advancing by 1 to 2 degrees to the pinging can be heard then back off timing to last position with no pinging. Hope this helps
    Regards Col

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    The dwell angle for all Renault 12 Australian Bosch distributors is 48+- 2 degrees.

    Note that the distributor spindle can wear so check for any axial play, and that the internals can also wear causing running issues. Also it wouldn't hurt to replace the cap and rotor if they are looking worn too.
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    Quote Originally Posted by Simon View Post
    The dwell angle for all Renault 12 Australian Bosch distributors is 48+- 2 degrees.

    Note that the distributor spindle can wear so check for any axial play, and that the internals can also wear causing running issues. Also it wouldn't hurt to replace the cap and rotor if they are looking worn too.
    Agree with all those suggestions. I was going to post suggesting checking dwell, dynamic advance and distributor internals. These things are pretty bullet proof if set up properly. It is possible, not mentioned, to have issues with the 12V wires to the coil - check that the wires are tightly attached to the tags that press onto the coil terminals as a loose wire in a crimped terminal can give some pretty poor running.

    You might consider doing these things one by one so that if you fix it at the distributor end rather than carbie end, you actually know which action was the real solution. If you rush in and do everything at once, you'll never know...

    Good luck.
    JohnW

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    Thanks for the info.
    I have a dwell meter but the books i have only mention point gap.
    I retarded the timing to 0deg in an attempt to get home.

    I will start with the dwell angle,
    then timing.
    If need be cap and rotor.
    Then coil.
    Leads
    Then plugs.

    I don't think it is a carby issue as it was running well before i changed the points and condenser.

    Ian

  13. #13
    COL
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    Quote Originally Posted by IThompson View Post
    Thanks for the info.
    I have a dwell meter but the books i have only mention point gap.
    I retarded the timing to 0deg in an attempt to get home.

    I will start with the dwell angle,
    then timing.
    If need be cap and rotor.
    Then coil.
    Leads
    Then plugs.

    I don't think it is a carby issue as it was running well before i changed the points and condenser.

    Ian
    Hi Ian

    It sounds like you have got the timing out. Changing the point gap will effect the timing.

    The order to do things is to set the point gap/dwell angle then adjust the timing.

    Remember that the rotor turns in a clockwise direction so to advance the timing you will need to turn the distributor body anti-clockwise and vice-versa to retard the timing.
    Regards Col

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    Fellow Frogger! IThompson's Avatar
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    I'm not sure if it is related but I noticed the timimg light seemed to phase with the timing mark with either the cylinder 1 near the flywheel or 4 furthest from the flywheel. I don't think it is supposed to do that.

    Ian

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    That's normal; they are in sync - just one revolution off, in firing order.

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    1000+ Posts Frans's Avatar
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    Now I am not sure if I am learning something or if I can teach something, but seriously 2 degrees will never work and the engine will be not rev. My input will be to start at 10 degrees and then advance and retard from there. I agree with Col's method although start at 10 degrees. It will be good to have feedback from you on where the car actually started performing.

    Ian, it doesn't matter whether you do your timing on 1 or 4. Both will line up the same point on the timing marks. You will see that if you look at your HT leads now, and you start at true no 1 flywheel end, check them CW, the next one will go to 3 then 4 then 2. If you start at 1 waterpump side, and counting from the waterpump side then the next will be 3 then 4 then 2. This might be a bit useless info but I am trying to explain why 1 or 4 will work.

    Remember to disconnect and block the vacuum pipe when you check the advance of the distributor. The vacuum can cause wrong readings.

    Regards
    Frans.
    Old enough to know better
    Young enough to do it anyway.

  17. #17
    Fellow Frogger! bingham driver's Avatar
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    Two questions, did it play-up only after changing the points?, if so thats the fault area.
    Have you tried driving with the vacuum hose disconnected?, points moving with vacuum could connect/disconnect with throttle movement. At idle/full throttle = no vacuum = no point movement & points wire may be broken.
    Once I thought I was wrong but, I was mistaken

  18. #18
    Fellow Frogger! IThompson's Avatar
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    Yes the miss firing occurred after

  19. #19
    Fellow Frogger! IThompson's Avatar
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    Part 2
    Replacing the points and condenser.

    Sorry using the iphone app. Accidentally hit the reply button too soon.

  20. #20
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    Quote Originally Posted by IThompson View Post
    Part 2
    Replacing the points and condenser.

    Sorry using the iphone app. Accidentally hit the reply button too soon.
    Ah, check inside the distributor for accidental earthing of insulated braided wire inside the device.
    JohnW

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    I feel like the Snake Oil salesman from old Western movies when I bring this up.
    The use of a vacuum gauge tapped into a point on the inlet manifold. Obtain the highest reading by advancing the distributor at a moderate idle then retard the dizzy dropping the vac reading shown. Readjust idle, check timing with light, it will be as near as dammit to the book figure.
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  22. #22
    Fellow Frogger! IThompson's Avatar
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    Wildebeast,
    I am not sure what you mean.

  23. #23
    COL
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    Quote Originally Posted by IThompson View Post
    Wildebeast,
    I am not sure what you mean.
    Wildebeast means like this Classic Inlines - Tuning with a Vacuum Gage
    Regards Col

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    Fellow Frogger! IThompson's Avatar
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    Francine lives.

    Thanks all for your suggestions.
    It has taken me ages to find the time to fix my R12.

    I adjusted the points and timing again but still the mis-firing occurred.

    Just now i swapped the ignition coil out of my second R12. Francine is running smooth again.

    I suspected the ignition coil after my timing adjustments had little affect.

    On the weekend drive when she started to play up the ignition coil was scorching hot. This suggests to me the internal electrical insulation was breaking down and partially shorting out.

    So i will now buy a new coil cap and rotor button and hopefully have some smooth driving for a while.

    Thanks everyone.

    Ian
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  25. #25
    bob
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    G'day,

    bit late and the fault has been found, but.....

    Got caught with two froggies with an annoying miss which was tracked down to the action plate in the dizzy. In days of yore the makers used to provide a little bit of earthing braid for this lively component, as we got cleverer they decided to do away with this expensive little addition and found that they could rely on the wiping of a tired spring over grotty oily surfaces......

    They ran really nicely with addition of two inches of braid pinched from an old shielded cable

    cheers,
    Bob

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