Like the previous poster started you cannot remove the cinch pin on Thunder Tiger engines with the carb still in place.

To Remove the Carb:

loosen the hex nut and back it off just one thread but do not remove. The nut will be just slightly away from the case. Now using a small wood dowel that will fit the end of the threads without pushin on the nut and a small mallet gently tap the dowel just once and the cinch pin will move in slightly up to the nut. Do nothing more on the pin or nut.

Just rotate the carb to loosen and it will now easily pop out. Not sure what damage you have done but the pin and nut will now most likely need replacement. I would recommend calling you LHS first as these parts are not carried by many shops.

John