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Thread: Runs rough on cruise

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    Experienced Lancista carcrank's Avatar
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    Runs rough on cruise

    I have an S2 Coupe it accelerates and idles well but when sitting in top gear with a light throttle in the 80 - 110 KPH range it feels "woolly" or rough. I have installed an electronic ignition but it was doing it before I did that, I have checked the leads and replaced the rotor, the cap looks like new I have also replaced the plugs with Denso iridium but no change . It has been suggested the fuel pressure may be too high (I'm running a standard mechanical pump) making a bad needle and seat leak.

    I am going to do an other compression test in case a valve clearance in closing up. Any other ideas?

    Also it is definitely getting worse.

    Cheers

    Mark

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    Legendary Lancista lancialulu's Avatar
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    Re: Runs rough on cruise

    You can check valve clearances, but what fuel are you using and on a light throttle the idle circuit in the carbs is still in play and with the higher volatility of modern fuels you may need to up the idle jet size. Just a thought...

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    Experienced Lancista tangmonster's Avatar
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    Re: Runs rough on cruise

    my 2c

    it is always something simple.

    When last was the carb balance checked?

    No need for expensive tools to check it.

    My aquarium pipe with 2 stroke oil and nipples with o rings at the end works perfectly well.

    carb balance is much more important at lower throttle position than WOT.

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    Experienced Lancista carcrank's Avatar
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    Re: Runs rough on cruise

    Yes after jumping to all sorts of complicated conclusions I think it will be something like balance or idle mixture, thanks.

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    Experienced Lancista AB095's Avatar
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    Re: Runs rough on cruise

    I could not balance my carbs. Took it to a carb specialist & the butterflies were worn. The throttle action caused the spindle to try to move the butterflys laterally as well as open them so wearing the butterflys as well as the carb body. Body was milled round with new butterflys made up to suit. Cost a bomb but now idles beautifully even at 550 rpm.

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    Experienced Lancista carcrank's Avatar
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    Re: Runs rough on cruise

    My rough running while cruising continues.

    I have replaced the whole ignition system with no result.
    I have bought vacuum gauges and checked the carburettor balance, it is now correct.
    I have checked the idle mixtures with 4 Colortunes and they are OK.
    I have checked the float levels using Marnix's device, they were within spec (18mm)
    I have rechecked valve clearances.

    A friend suggested that the car may have weak or broken valve springs, but it does rev out to the redline so that's unlikely.

    I think I will recheck my valve timing.

    Lastly I have an Air Fuel ratio gauge that I have temporarily rigged up (It screws into a 14mm hole I fitted in the exhaust pipe just after the 2 into one) and on idle and overrun it's reading about 13.5:1 but when running it's all over the place and very lean sometimes out to 17:1. on cruise (but sometimes not) and also it has been 16:1 -17:1 when hesitating coming out of sharp corners.

    Any help appreciated.

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    Re: Runs rough on cruise

    Quote Originally Posted by carcrank View Post
    My rough running while cruising continues.

    I have replaced the whole ignition system with no result.
    I have bought vacuum gauges and checked the carburettor balance, it is now correct.
    I have checked the idle mixtures with 4 Colortunes and they are OK.
    I have checked the float levels using Marnix's device, they were within spec (18mm)
    I have rechecked valve clearances.

    A friend suggested that the car may have weak or broken valve springs, but it does rev out to the redline so that's unlikely.

    I think I will recheck my valve timing.

    Lastly I have an Air Fuel ratio gauge that I have temporarily rigged up (It screws into a 14mm hole I fitted in the exhaust pipe just after the 2 into one) and on idle and overrun it's reading about 13.5:1 but when running it's all over the place and very lean sometimes out to 17:1. on cruise (but sometimes not) and also it has been 16:1 -17:1 when hesitating coming out of sharp corners.

    Any help appreciated.

    Hi Carcrank

    Your AFR radings are way to high up in the rev range, I think it is so lean you could get damage to your engine.

    Could it be that you have a problem With fuel starvation at higher speeds? Your engine and carbs could be ok, but either you ave a malfunctioning fuel pump or clogged lines/fiters before the carbs. If the jets in the carbs gets dirt in them it usually stays there until you clean them, it would not fluctuate as you describes.

    When you Close the throttle on overrun, the vacuum helps pull sufficient amount of fuel through Your carbs. So then Your AFR are about rigth. On part throttle opening and high throttle opening you are in a lean condition.

    I would also check the acceleration pumps actual output values according to the manual.

    Tor

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    Re: Runs rough on cruise

    Mark, a relatively low cost check would be to replace your iridium plugs with copper plugs. The engines in these older cars, with their low voltage distributor based ignition systems, were never designed to fire iridium plugs. Get a new set of copper core plugs, gap and install and then take it for a drive.

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    Experienced Lancista carcrank's Avatar
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    Re: Runs rough on cruise

    Quote Originally Posted by 4thinline View Post
    Mark, a relatively low cost check would be to replace your iridium plugs with copper plugs. The engines in these older cars, with their low voltage distributor based ignition systems, were never designed to fire iridium plugs. Get a new set of copper core plugs, gap and install and then take it for a drive.
    Yes I thought that as well and have installed a new set of standard plugs gapped at .022", sorry I should have put that in the list.

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    Legendary Lancista Marnix's Avatar
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    Re: Runs rough on cruise

    Very hard to do remote diagnosis, but a few guesses.

    I personally find 18mm fuel level a bit on the low side; depending on the type of carbs, it is at the very low limit, or even over it for the older style. I personally don't go lower than 19mm, and I prefer to have it at 20mm for all types (for the older types, 20mm is dead in the middle of specs, for the newer ones, it is at the high limit of their 19mm spec). I would bend it very, very slightly to get a bit more. The bending works very sensitive, with bending I mean a really very small fraction.

    The old ignition system of the Fulvia is a weak point of the car. One thing that is often overlooked is the capacitor in the distributor. It is something that with age starts to intermittently fail under certain conditions, giving all kinds of weird symptoms. The trouble is that is rarely completely fails, stopping the car completely, which would be easier to find as a fault. It looks like a detail, but the capacitor is very much an essential part.
    Lancia Fulvia 2C 1964
    Lancia Fulvia Coupe Rallye 1,3 1968
    Porsche 924 1979
    Alfa Romeo 33 1.4IE 1993

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