I had my front carby float stick open once. It was a simple matter of taking the float chamber lid off (four screws) and bending the small metal tab so that it will engage the fuel valve sooner. I suspect this is not the case for you however as you did not complain about fuel leaking from the throat of your carby, which is what I experienced.
If I were you I would replace all the plugs with NGK BP"5"ES (5 means hotter, and many people on this forum have agreed that the hotter plug is better for a road car). At the same time I would also replace your leads, just to be sure it's not them. It is also possible that your dizzy needs a new cap, so I'd replace this at the same time. If you have ever considered putting an electric dizzy on the car, this would be the perfect time. Everyone here agrees they make a big improvement to the engine.
I'd also suggest checking the valve clearances on your engine. If you haven't done it before it is probably better to get someone to show you rather than trying to learn from a book.
If your front three cylinders are still running rich after this then I'd be taking it to a specialist again.