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Thread: Weak spark?

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    Mechanic Grandaddy_low's Avatar
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    Default Weak spark?

    Hi,

    I have just replaced the dizzy cap, rotor arm, points and HT leads on my 2.25 S3. Around about the same time I replaced the manifold to head gasket and the inlet to outlet manifold gasket where the stove is.

    However it sometimes seems to be running rough at idle. It will run fine for a few seconds, then a little rough. If you use the footbrake while it is running rough, its enough to kill the engine. It runs fine at higher revs - pulls normally.

    I have turned up the idle speed a little but its still won't idle smoothly. I checked the gap today and altered it ever so slightly, but not change. I tried a technique I saw once of pulling a HT lead off and holding it with a screw driver near an earth. The varied between orange and bluey orange.

    I read on other posts about greese on the breakers when new, but its done about 80 miles since so it should have burned off?

    I also wondered about carb freezing - I did observe a little ice forming on the lower butterfly valve...

    Any ideas? Cheers, GDL.

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    Defender of the Forum. TEMPL4R's Avatar
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    Default Re: Weak spark?

    If you have a servo, that will be altering the revs when you press the brake. Check for leaks at the manifold.
    If it didn't do it before you did the work, it's something you have done.

    Chris
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    Default Re: Weak spark?

    I think if you pumped the brake while it was ticking over, there was always a brief, but noticeable change in the revs because of the 'drop' in vacuum. I have looked around the new gaskets for leaks but can't see/hear anything. I would expect that if it was leaking at the head to manifolds gasket, one spark plug would be a different colour, but they are all the same: sooty.

    If the gasket between the two manifolds were failing I'd be able to hear it as its the exhaust gasses that would be escaping I think...

    Given that I can't see or hear anything wrong with the new gaskets I am inclined to believe that its something to do with the new ignition parts... especially as its intermittent.

    But yes - I'm sure its something I've done I was always taught to do one thing at a time and check it in between... but I got impatient waiting for parts so started on the next bit. Lesson learned.

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    Default Re: Weak spark?

    If you don't wipe the contacts to clear the oil or grease, after a while it starts to melt or burn, the contacts don't make and break properly, give them a clean before you go any further, that will cancel that from the equation.

    Sooty plugs is too rich, wrong grade plugs or a bad spark.

    If the intake was leaking, the carb might have been reset to try to counter that, so could be set up too rich now you have sealed all the leaks.

    Give the points a clean. If the ignition parts were Intermotor, change them to Lucas.

    Chris
    ........Such are they, whom God chooses for Himself, and gathers from the furthest ends of the Earth, servants from among the bravest, in Israel, to guard watchfully and faithfully, His sepulchre and the Temple of Solomon, sword in hand, ready for battle.
    YCHJCYA2PDTHFH and PhD Hons Drvl Cleckheaton and Grand Master of the Forum Lodge of Enlightenment

    Everyone is entitled to their opinion, the trouble is, yours is ridiculous.

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    Default Re: Weak spark?

    Quote Originally Posted by TEMPL4R View Post

    Give the points a clean. If the ignition parts were Intermotor, change them to Lucas.

    Chris
    Lucas - Prince of Darkness I don't think they were Intermotor,as it was not a yellow and blue box, but it was not a green box either so if cleaning does nothing, I'll try that.

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    Default Re: Weak spark?

    I have tried cleaning it up. Maybe a slight difference, but the problem still exists. When you pull up, it idles fine for a few seconds, then suddenly the revs drop off and it runs rough.

    There are two plates below the points and the condenser. They are secured to the distributer body with two screws. The two plates rotate in relation to one another when the points are loose however they do not when it is secured... I know the points should stop moving when the screw is tight, but should plates be held solid too because it looks like they should move...

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    Default Re: Weak spark?

    So it turns out that the problem is a spindle to the carb. There was some play in the linkage where it attatches to the main spindle. Most of the time it was not going all the way to the throttle closed position, hence the idle had been turned down. This meant that when it recieved a bump, especially green laning, the throttle closed properly. It was just hovering above the point of stalling. Pumping the brake pedal was enough to lower the vaccum in the inlet manifold and stall it.

    That took a while to diagnose!!!

    Cheers, GDL.

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