1973 Series 3 2+2 V12 Not running on all cylinders

Talk about the E-Type Series 3

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jfjharry
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#1 1973 Series 3 2+2 V12 Not running on all cylinders

Post by jfjharry » Wed Nov 23, 2011 11:00 pm

The car does not run on all cylinders when first started. I'm guessing 11.
We need to do a few km's before it comes good. Before I waste time trying to tune it I was going to give it a compression test. I have not done a car for years but I assume its only a matter of holding the throttle open, ignition disconnected and read the compression from each one after 8 seconds with the motor turning over. I was actually going to do this test cold because this is where the trouble is. I would be interested to know if anyone else has had similar troubles and is this a good idea or not!
Harry

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alexb1406
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#2

Post by alexb1406 » Thu Nov 24, 2011 11:22 am

If it comes good after a few kms it's unlikely to be a mechanical problem. It is more likely to be something simple like a spark plug or lead, or at the worst something to do with the Opus ignition system.

Try this - when you first start it up remove each plug lead in turn taking the necessary precautions and hold it just clear of the plug so the spark has a gap to jump before it reaches the top of the plug. If it comes good and then gets bad when you replace the lead it is a sure indication of a bad plug. Even if this doesn't work it does not mean the plug is good but usually it does work. You may find it easier to do this at the distributor end - this will lessen the risk of shock as there will be no voltage in the lead when you pull it away from the distributor, just be careful when you move it closer to see the spark. At the very least it should pinpoint which cylinder is misfiring - then try swapping plugs or leads and see if the problem moves with the part you swapped. Sometimes just cleaning the plugs cures the problem.

If you are a little nervous about doing this remove all the plugs after running it while it's bad, before it gets good, and all the tips should be dry - if one looks shiny and a little wet this is likely to be the bad plug.

Of course a compression test won't hurt and you can do it exactly as you described.

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jfjharry
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#3

Post by jfjharry » Fri Nov 25, 2011 6:25 am

Thanks for the information. On the reasons for the compression test I was thinking on the lines of a 'sticky valve', but then again I've had no experience on these cars. I will try your plug lead removal test first. I have also noticed that the dash pots in the carby's tend to loose their oil in a short period [possibly a month or two] regardless of whether the car is used. I wonder if this has anything to do with the running when its cold?
Harry

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vee12eman
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#4

Post by vee12eman » Fri Nov 25, 2011 11:05 am

Hi there,

Oil draining from the dashpots is a definite disadvantage of the Strombergs, even with a rebuild kit; mine do the same. I am still investigating solutions, does anyone have any ideas?

The main problem this causes is during acceleration, when the lack of oil allows the dashpot pistons to rise too quickly and the mixture leans off, causing poor acceleration and or hesitatancy. Once at a steady RPM, there is little or no effect once the mixture stabilises.

I am not sure what oil to use - some say engine oil, others say use a special dashpot oil - problem with that is it tends to be a little thinner than the engine oil and therefore drains quicker... Any recommendations from others out there?

Regards,
Regards,

Simon
Series III FHC

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SESH
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#5

Post by SESH » Fri Nov 25, 2011 2:31 pm

I have a similar problem with mine. I did have one of the front carbs sorted with a new seal in the dashpot, which helps, but they still need regular topping up. I was told to use 3 in 1 oil, but that is pretty thin so will leak fairly easily. Was also told that ATF fluid is ok to use too.
Mike

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jfjharry
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#6

Post by jfjharry » Sat Nov 26, 2011 2:07 am

Hi Mike & Simon
I've been topping up my carburettor pistons as per the V12 workshop manual - it says to use ZENITH BLUE PACK or S.A.E. 20 engine oil to within 6mm of the top of the rod - hope this helps.
Harry

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vee12eman
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#7

Post by vee12eman » Sun Nov 27, 2011 8:38 am

Hi Harry,

Thanks for the posting - I have been using 20/50 grade oil (as in the engine) and this has been better than the carb dashpot oil I originally bought. This was fairly thin but a close look at the label revealed it was for pre war SU carbs, so possibly not suited to my 1971 V 12 E. Anyhow, went for a drive today to the JCCV Concours and the car purred along, albeit with just a little hunting. I realise now that I forgot to top up the dashpots, but I think the problem is that the mixture is a little weak as the car ran more smoothly with a tiny pull on the choke cable. Also, under acceleration, when the car is effectively being over-fuelled, the problem went away - regardless of choke position. I will have another play next week, but the good news is that the 5-speed Getrag kept fuel consumption down and on the freeway I used far less fuel than anticipated.

Regards,
Regards,

Simon
Series III FHC

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AussieEtype
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#8

Post by AussieEtype » Sun Nov 27, 2011 10:06 am

If it is not running on all cylinders it will not be the dashpots in the car (the issues of low oil will impact all cylinders - most likely a dodgy spark plug - can be caused by a valve stem seal leaking when cold allowing oil into a cylinder and oiling up the spark plug until it gets hot.

Pull the spark plugs and you will most likely find one with different burn characteristics.

Likewise you may just have a failed spark plug - test them.

Garry
1971 Series 3 E-type OTS
1976 Series 2 XJ 12 Coupe

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alexb1406
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#9

Post by alexb1406 » Sun Nov 27, 2011 10:29 pm

I'll second that, dashpot oil will not affect cold running, it is there to richen the fuel mixture when accelerating. Valve stem seal is possible as is a sticky valve, but I'd put my money on a plug, especially if the car does not get used regularly.

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