Citroen SM not starting, NGK spark plugs
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  1. #1
    Fellow Frogger!
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    Default Citroen SM not starting, NGK spark plugs

    My SM doesn't get used a lot (I prefer fanging about in a 18 YO Peugeot 306 S16, one of David Cavanagh's "too good to wreck" cars). I started it a couple of days ago no problems but when I went to start it today it just refused to co-operate.
    Checked, yes there was fuel at the carbs. Yes there was a spark from a plug lead to the cam cover, both banks. OK, has to be plugs.
    This was odd as I had fitted new NGK Iridium BPR5ETX plugs not all that long ago. These are supposed to be a superior plug to conventional plugs and you can read about how good they are at NGK Spark Plugs Australia
    Swapped them for a set of normal NGK BP5ES plugs and it started instantly.
    I'm not sure what conclusions to draw from this. The Iridium plugs did have black sooty deposits and maybe they are not hot enough for the way I use the SM.
    roger

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  2. #2
    Real cars have hydraulics DoubleChevron's Avatar
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    All 6 plugs Does the SM has that difficult to setup "twin point" distributor like some old V8's do I bet a modern distributor like a 123 conversion would transform the way it starts and run.

    SM

    I bet someone on the SM list has tried them.

    seeya,
    Shane L.
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  3. #3
    1000+ Posts bluey504's Avatar
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    Iridium and other rare earth plugs are best used with electronic ignition systems. The greater voltage 'seems' to get them hot as they have very small electrodes and loose any retained heat quickly. The old style plugs had a fairly hefty mass to hold heat. All of this is said with out seeing both plugs side by side, Folks this is the disclaimer done! NGK also do a V-groove type which I've found to work a treat on points systems. Not very helpful I know but my . Brendan....I want an SM!

  4. #4
    1000+ Posts alan moore's Avatar
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    I fit NGK Iridium plugs to all my vehicles and bikes. Some of the bikes have points ignition, others magneto. The cars are a variety of standard to very modified. I have never had any problem with the plugs, and found particularly that the magneto bikes started and run better on them. I would think 5s would be plenty hot enough for the SM. I run 7s in my Renault "750", 7s in the GTA Turbo, 8s in the BMW 2002 race car, and 6s in my stock BMW R60/2 bike.

    The theory at least is that the very small electrode is going to be able to fire and stay cleaner because of its size. Perhaps they have been fouled through a too rich mixture and slow running, and a hit with some contact cleaner would restore them. I generally use the gap specified by the manufacturer.
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    Funny you should mention this. We had to change the plugs in the 3.0 carb SM at the weekend.

    After a trouble free weekend of running over 600kms a couple of weeks ago, the plugs came out black and smelly and a little damp when she just wouldn't start. It's so easy to flood this thing with the three carbs pouring petrol into the cylinders.

    I think the plugs were approaching 10,000kms in service, so were due for replacement anyway. We used NGK StandardBPR6ES. (I pulled out 5 Denso's and one of these when I replaced them.)

    There are some other NGK's available, including:
    V-PowerBPR6EY
    G-PowerBPR6EGP
    Iridium IXBPR6EIX

    I too was wondering of the Iridium's would be better, but (this time) went with the standard.

    Shane, I'm not too sure whether there is universal acceptance that a 1-2-3 is the be all and end all. Some owners have reported running rich, and they don't always deal well with the heat. But lots of variables. I have one fitted (to this and the Safari) so will persist...





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  6. #6
    Real cars have hydraulics DoubleChevron's Avatar
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    Quote Originally Posted by pajamas View Post
    Funny you should mention this. We had to change the plugs in the 3.0 carb SM at the weekend.

    After a trouble free weekend of running over 600kms a couple of weeks ago, the plugs came out black and smelly and a little damp when she just wouldn't start. It's so easy to flood this thing with the three carbs pouring petrol into the cylinders.

    I think the plugs were approaching 10,000kms in service, so were due for replacement anyway. We used NGK StandardBPR6ES. (I pulled out 5 Denso's and one of these when I replaced them.)

    There are some other NGK's available, including:
    V-PowerBPR6EY
    G-PowerBPR6EGP
    Iridium IXBPR6EIX

    I too was wondering of the Iridium's would be better, but (this time) went with the standard.

    Shane, I'm not too sure whether there is universal acceptance that a 1-2-3 is the be all and end all. Some owners have reported running rich, and they don't always deal well with the heat. But lots of variables. I have one fitted (to this and the Safari) so will persist...





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    I was thinking the hotter spark of an electronically produced spark might help keep the plugs firing. If they get wet and sooty 'cos it drains off when hot, no ignition system is going to help that.

    I wonder if the injected ones suffer from difficult starting (without 3 carbs leaking fuel into the motor).

    seeya
    Shane L.
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  7. #7
    1000+ Posts bluey504's Avatar
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    Quote Originally Posted by alan moore View Post
    I fit NGK Iridium plugs to all my vehicles and bikes. Some of the bikes have points ignition, others magneto. The cars are a variety of standard to very modified. I have never had any problem with the plugs, and found particularly that the magneto bikes started and run better on them. I would think 5s would be plenty hot enough for the SM. I run 7s in my Renault "750", 7s in the GTA Turbo, 8s in the BMW 2002 race car, and 6s in my stock BMW R60/2 bike.

    The theory at least is that the very small electrode is going to be able to fire and stay cleaner because of its size. Perhaps they have been fouled through a too rich mixture and slow running, and a hit with some contact cleaner would restore them. I generally use the gap specified by the manufacturer.
    Alan I think we are both chasing the same rabbit. The small electrode does stay cleaner but does loose rapidly. Too rich a mix will 'wash' the plug with unburnt fuel and a few revs is always a good thing IMHO! Magneto systems are the equivalent to modern electronic systems just a touch less subtle.....Still can recall the jolts when I was a tad careless! A touch OT the wildest combo of ignition I've ever come across was in ZD Fairlane running a home built Nascar motor, as you do, with a MSD into NGK Mazda rotary race/2 stroke race plugs B9EGV (?). Two tonne of very fast whatever. Brendan.

  8. #8
    1000+ Posts alan moore's Avatar
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    The 750 does run a Capacitor Discharge Ignition, which is of my design and build about 28 years ago when doing Electronics at TAFE. I still use a normal coil, and the output in Joules is probably no more than the original system, but the voltage is huge and will easily jump a 25mm gap. I originally had this ignition on my Webered 15TS, and it helped in stopping plug fouling whilst running slowly with a big cam. It still uses points to trigger it, with my reason at the time was that I just had to change over a plug on top of the unit when I believed the CDI would inevitably blow up, and it would be back to standard ignition.

    The BMW 2002 runs an M4 Motec and uses two double ended coils with wasted spark. So it is not really an everyday system either, with the motor having a huge 316 degree cam and rest the rest to go with it, it never misses whether at low revs on the road or on the track. The plugs have been in for 2 years, but maybe only 1000Klms, 500 of which were on the track.

    As you might have worked out I do like NGK Iridiums.

    Magnetos don't produce very good spark at low revs, like kick starting, and this is where I think the Iridium plug really helps.
    '56 Renault 4CV (16TS Power)
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    '82 Renault Fuego GTX
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  9. #9
    Real cars have hydraulics DoubleChevron's Avatar
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    Here's a thought .... Is there a manifold drool tube on it If so, some "helpful" person hasn't blanked it off have they ..........................

    seeya,
    Shane L.
    'Cit' homepage:
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    Proper cars--
    '85 Series II CX2500 GTi Turbo I
    '63 ID19 http://www.aussiefrogs.com/forum/showthread.php?t=90325
    '72 DS21 ie 5spd pallas (last looked at ... about 15years ago)
    '78 GS1220 pallas
    '92 Range Rover Classic ... 5spd manual.

    Yay ... No Slugomatics


    Modern Junk:
    '07 Poogoe 407 HDi 6spd manual

  10. #10
    DS
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    My Safari has done this a few times when I've used cheap fuel. Black sooty and a pig to start and have run. All I can do is fit new plugs.
    Citroen Car Club of New South Wales member.

    My Citroen ID21F can be seen here http://www.flickr.com/photos/frontdr...7605999522616/

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