Miss-fire and sooty spark plugs

[Woodruff]

Hi, I'm hoping for some ideas as I am not too familiar with the twin cam engine.

I am working on a '72 +2 with a big valve engine. When it arrived it had not run for several years and number four spark plug hole was stripped.

The head was taken off and sent away to be repaired.

When it came back the engine was almost impossible to start so on advice the worn Delorto's were replaced by a set of new Webber 40's.
The car was then tuned on a rolling road where the- as it turned out badly- repaired spark plug hole let go ad the 'plug shot out and hit the roof. The tuner araldited the 'plug back in to complete the tune up and informed me what he'd done.
When back in the workshop, the head was sent back to the engineers who this time did the job properly. Once re-fitted the car began to start and run reliably.
However due to other work being done on the car it's a year on now and the car has only just gone for it's first MOT ( on a recovery truck).
My problem is that although it idles fine, when you ask the engine to do any work on the road, it throws thick sooty swirls of smoke out of the exhaust and the plugs instantly soot up. Also, the engine misfires, spits through the carbs and back fires.

What's going on?

I have checked the coil and plug leads, they're OK. There is an issue with fuel supply but I don't think that it's a contributing factor. The carbs have not been touched since tuning and I can't see both of them going out of tune at the same time with virtually zero miles covered.

It has been suggested that either the old Sparkright Ignition is breaking down or that I am a tooth out on the cam but how can I tell?

Suggestions appreciated.

[EPA]

The cold start device may be stuck partially on,most people don't use the choke to start their cars as a few pumps on the accelerator is all that is required
Ed

[Woodruff]

Thanks, I'll check this out although it is looking more and more like one of the cams is a tooth out.