Jetting For Original Exhausts

You will need to check the carb numbers ( etched on the side of the carb ) and select the correct ones to pick your parts, mains & pilots on the first two types ( items 11 & 14 ) or the third type mains only. All three carbs in the set take the same jet sizes but each type are different sizes.

http://www.worldoftriumph.com/triumph_motorcycle_parts_catalogue?model_id=16485

 

I've never run a Thunderbird so cant honestly say, but, you could give it a go and check your plugs after a run that gets the bike up to temp then kill the motor at cruising speed somewhere you can pull over and remove a plug and see if the colour is OK .

Maybe someone else has better experience of your bike and its setup