Loss of power & fouling spark plugs

[leifanten]

Hello All,
my twincam is acting up. I could really use some second, third and so on opinions. (I am not sure my dear wife will come to my rescue at 10pm next time, so I would like to try and fix this before I hit the road again.) I also have a keen appreciation of the lightness of our cars. It is a piece of cake to push (Especially in flat Texas). Now, to the problem at hand:

Symptoms:
from cold it runs fine for about 30 minutes
then it has sudden and complete loss of power. It feels like it is running on two cylinders
when left to cool / idling it recovers but only for a brief session (1-2 minutes) before it plunges into despair again
Spark plugs on 1 and 2 foul up even when using the hottest rated plugs - suggesting that I might need to drop the needle on front carb. (But is that significant enough to cause all this?)
Does not misfire significantly, just sounds out of breath when attempting to pull away
At the worst of behaviour it will not even idle

Facts:
recent cylinder head off/on to replace broken head stud
new bp5es spark plugs
new plug leads
new dizzy cap and rotor
On strombergs that have been professionally rebuilt by Paltec/Micropolishing.
Carbs balanced using acoustic tube to ear method
Compression 170psi on all cylinders on three to four revolutions
Runs at 85 deg C
Ignition at 10 deg BTDC
runs luminition electronic ignition
Electrical fuel pump with pressure regulator at 2.5psi
New fuel filter
Fresh fuel

I am running out of ideas, so anything to set my creativity off would be great!

[ringe]

Leif,

my vote goes to a thermal problem in the electronic ignition.

Check for good sparks at the plugs. I had the same symptoms years ago in a VW Beetle (no Lumenition though) and reverted back to points.

Matthias

[robertverhey]

Just looking at the work you've done / had done recently, you should be able to narrow things down by:

Putting the old dizzy cap and leads back on (hairline cracks tend to open when things get hot)
Swap front two and rear two plugs

Swapping over potentially offending carby parts front to rear, eg needle, and see if the prob goes with it.

That should allow you to eliminate a few obvious things before delving deeper....

[andyelan]

Hi Leif

I had exactly these symptoms on my Europa and it turned out to be the insulation in the coil braking down when it got hot.

One tell tail sign, if it is this problem, is that the engine will first begin to misfire when under load under load as this is the time when the ignition has to work hardest to fire the plugs. Also, if the bonnet is opened for a few minutes allowing the coil to cool, all should be well again for a while untill it heats up again.

Regards
Andy

[paddy]

Try fitting 4 colortunes and watch what happens when it warms up. At least I would think you could determine if it's fuel or ignition.

Also just put a timing strobe on it to confirm nothing is going wrong with the timing.

Has anyone tried with one of those freeze sprays to isolate this kind of problem?

http://www.dse.com.au/cgi-bin/dse.store ... View/N1122

Paddy

[leifanten]

Thanks All. It is hard to keep creativity flowing when you are busy tearing you hair out..... I am going to try these things in an order to be determined and let you know how it works out.

[ppnelan]

On strombergs that have been professionally rebuilt...

Beware of ANYTHING that has been 'professionally rebuilt'...
Strombergs are simple in principle but rely on fine tolerances in many parts for proper performance. If temperature compensators are fitted, are you sure they are working correctly? You could try removing & blanking them off to see if the symptoms remain. It would at least 'eliminate them from your enquiries'...

Matthew

[leifanten]

Thanks again for all the help! I have replaced the coil and that took care of the death by heat problem. I will get my hands on a haynes book for the strombergs, because I suspect the fouling of the two front cylinders to be caused by the jetting needle needing to be lowered slightly on the front carb.

Now, on another note, I discovered whilst doing all of this that the clamp that holds the dizzy in place does not do that..... The screw is tightened all the way and it turns out that it does not squeeze the dizzy the way it is supposed to. This leaves room for some creative movement by the dizzy, and must be fixed, so that will further improve the sustainability of fine performance.

Anyhow, I will have to tear the head off to fix a leaking water pump, and that means fixing the dizzy fixture will be infinitely easier. Every cloud has a silver lining.

Back to work!

[curly type 26]

Hi Leif, is it because the base on the dizzy has collapsed? I know someone is making a much thicker alloy clamp to deal wth this problem might be Burtons or phaps QED would save replacing distributer. Hope some help Curly

[leifanten]

I am not sure why it let itself get completely compressed. If it is shot I will go ahead and buy a new pertronix dizzy and put the luminition in my cortina 1500 GT.

[leifanten]

the base had collapsed. new pertronix dizzy ordered.

[curly type 26]

Result, just make sure you just nip it up, as so easy to over do & thin alloy skirt at base eventually fractures & collapses Curly