Woofa Express looking for help.

[woofa.express]

Woofa Express needs help.

Woofa.Express, my ,28 ute, has never run perfectly since I had a major service. What turned out to be a service was a partial strip and rebuild. The workshop was a well-known and deservedly respected. The old gentleman principle even did white bearing pours. He had rebuilt the engine in my Tourer and that has run perfectly for years. Well he had sold his workshop at Dookie, Vic, and whilst he was on premises when this was serviced he was not consulted.
Well now the performance has deteriorated. It starts so well, idles well and cruises well but keeps missing and back firing and is jerky when accelerating at any speed. Always.
Fuel consumption less than 10 mpg. Spark plugs black in short time, much blacker than Al Jolson’s dial. Even when mixture is screwed to full lean. Have changed main jet and needle and seat, that’s what I had on hand. Carby doesn’t have venturi.
Have substituted the coil for a known serviceable one. Plugs are modern long reach NPK BP5ES. Done less than 2,000 miles. Do I have the correct ones? I substituted the original plugs by adding a reducer bush. Both supplied by Snyder’s.
I feel exhausted and am asking for help. And in anticipation, thank you.