Flaminia V6 engine, single solex twin barrel carb - sparking problems

[FERGTS246]

Hi All,
I’m having repeated problems with my engine not running properly.
I’ve had spark plugs stop working, sparks leaking through rubber plug caps and creating a tiny hole in them. I’ve replace the bad spark plugs and the rubber covers.
The engine runs great immediately afterwards but then a couple of days later, after driving the car couple of times for short distances, the engine runs badly again!

Now, in the order of the cylinder firing sequence, cylinders 3, 5 and 6 aren’t firing - (see diagram attached). I can tell because the exhaust manifold branches for these cylinders aren’t getting hot whilst the others are.

I’ve got:
‘Ignition123' Electric Distributor Ignition system
Carbon core HT leads
NGK iridium spark plugs (NGK BKR6EIX 6418 Spark Plug Iridium IX)
Standard spark plug rubber caps.

The position of the cylinders not firing don’t suggest a blocked carb main jet. I’ve had a problem with blocked fuel pipe and/or weak fuel pressure but I’m pretty sure that has been solved now.

Do you think its possible that 123 Ignition system, carbon core HT leads are damaging the spark plugs and rubber caps?

Any other suggestions please?

[Richard Fridd]

When 'the engine runs badly again', assuming the plug caps are not leaking sparks, are the plugs still sparking? I have recently bought a small spark plug test machine for bench testing suspect plugs. Also, a bit tedious, but does swopping leads/ plugs around 'move the problem'? Richard

[lancialulu]

While I have no direct experience of 123 ignition systems I have heard they "eat" spark plugs on some cars. The system seems to generate much hotter spark as it requires a more powerful coil. Maybe it is finding ways to ground due to the carbon leads. An interesting experiment would be to run the engine in the dark with the bonnet up to see if the is any arcing.

[FERGTS246]

Thanks for both your suggestions. I'll try them all tomorrow.

If they don't flag up the issue, I'm also wondering if the carb float level is a touch too low or the fuel delivery is just on the edge of being too low in terms or flow and/or pressure, that the cylinders creating most suction on intake will be greedy and take all the air/fuel mixture leaving some without any?

Thoughts anyone please?

Chris

[Charles Frodsham]

Hi Chris

I run a programmable 123 Ignition system on my Flaminia. I don’t think there is anything intrinsically problematic as long as the timing is correct. Do you have the correct coil?

“Carbon cored” leads. Are these Silicon leads? Have the ends been properly manufacturered......not screw in?

Have you done a compression test?

What fuel pressure are you supplying to the carb, and is it filtered? It’s certainly worth looking at carb float level etc.

Sometimes if the plugs are heavily fouled they are unsalvageable, however the Iridium plugs you are using are fairly good. Have you tried cleaning the plugs again? Do the cylinders not firing have particularly oily plugs?

I note you say this happens after short journeys.....how short? These cars like to be run up to temperature properly and driven a decent distance. Repeated short journeys can cause plug fouling, even with Iridium plugs.

Cheers Charles

[FERGTS246]

Hi Charles, thanks for your reply.

I have the Bosch coil supplied and recommended by 123 Ignition. The leads have a carbon core (about 1 - 1.5mm dia.) with crimped terminals.
Haven't done a compression test since the 123 Ingition dizzy was installed (23 months ago); it was very good and all cylinders were within 5 psi of each other. I think they were all around 195psi or was 95psi - whichever it was, I was told it was good.
Jouneys have been between half and mile up to 5 miles to test the car.
Over the 2 months I've had these recent problems, the cylinders not firing have varied. No obvious oiliness on the plugs.

I managed to get it running on all cylinders on Sunday after de-carbing the plugs (by burning it off with blowtorch) but it has now developed a back fire through the carb on tweaking the throttle. After checking for vacuum leaks, the vacuum tubing, checking the tappets, cleaning jets and checking float level, its now not firing on one cylinder and still has a back fire, though less often.

Setting tappets
The tappets were set at about 0.06" exhaust and 0.03" intake. The shop manual I have specifies 0.1" exhaust and 0.06" intake so I changed them to that - now there's an obvious tappet clatter!
Do you know if the 823 series, single carb, 2.5 engine would be different to 0.1" exhaust and 0.06" intake spec'ed in the shop manual?

Thanks

Chris

[Neil]

Have you checked the voltage out of the dynamo/alternator? I understand there is a safety feature in the 123 if the voltage exceeds standard values it can shutdown the 123 unit, as you have some sparks on some cylinders perhaps that is not the issue, but worth a check.

[Richard Fridd]

'Running on all cylinders after decarbing the plugs'. If this is soot deposits, could it be a over rich fuel problem? Maybe in the carburettor's slow running circuit? I have checked my mixture with a 'colourtune' and found an improvement in flame colour by first cleaning the 'air bleed jets' and then making some larger air bleed jets to experiment with. I have increased the size of these jets from less than 1mm to 1.2mm. The 'volume control' tapered screws could then be adjusted with each increment in size of jet to suit. (Solex PAAI 40). My Solex tuning manual suggests air bleed jets to be twice the size of the pilot jets (0.55 in my case). These air bleed jets can be found by removing the carb top from the carb body, next to the pilot jet part of the casting. Also it did occur to me that a squashed gasket in that area could restrict air into this area. I assume the sparks have stopped escaping from rubber caps. Richard

[FERGTS246]

Neil and Richard,

Thanks for your advice. I'll check out all your suggestions

Interestingly, just before the beginning of these recent problems I put in a dynator from Wasp Performance (with built in regulator) that only uses the original regulator as a junction box. I'll check what its putting out and if it has peaks that the 123ignition might be shutting down.

Richard, do you have a specific tuning manual for the C40 PAAI? If so where did you get it please?

Lastly, do you know what the tappet gaps are for a 2.5 GT with Solex C40 PAAI carb. In my 'Shop Manual' it spec's - Exhaust 0.1", Inlet 0.06".  But on checking mine they are gapped at about - Exhaust 0.06", Inlet 0.03".
I reset them to what the Shop Manual said and now there's obvious tappet clatter.

Thanks in advance

Chris

[Richard Fridd]

I have adjusted my (2.5 PF coupe)tappets to 0.15 and 0.25 (6 and 10 thou) as in my workshop manual. The book which I have is 'Solex Carburettor tuning tips and techniques' (not specific to the C40PAAI but £10 well spent). Also the classic cars/modern fuels book is useful. Any misfiring which I had was from the exhaust rather than the carb. This was demonstrated by holding a postcard over the tailpipe, which would suck rather than blow each time the offending cylinder would try to fire with a sooted plug. Richard

[Charles Frodsham]

Hi Chris

Not sure if you’ve made a typo , but valve clearances are 0.006 and 0.010......as Richard said 6 and 10 tho’.......not 0.06 and 0.1

Or 0.15/0.25 mm.

Charles