It is a characteristic of ABC to be tight at TDC, it would be bad if not. Again, not familiar with TT carbs so I will stay out of that issue except to say mixture may well be the problem. You never said if it ever did idle properly before. If so, what happened to motor just before it changed to where it would not? ABC engines ARE in general fine engines. You might have a bad one but I doubt it and it should idle fine and have a good midrange and top end as well. Sorry, but I feel the guys at the field may have steered you wrong on this issue. I know it is hard to know who to trust at times. I have several of both ABC and ringed engines with no real preference for either type. Yer having a little bad luck, let's not blame a whole class of engine, OK?