MOPED ARMY

My girlfriend was riding her Trac Liberty with the M56 engine and she forgot to check her oil tank as it is the drip type with the oil reserve under the seat.

The bike stopped a couple of times on her, then i checked it and it was dry, i refiled the oil up and cleaned the carb, now her engine is doing a slight tap sound.

This might not be specific to that engine, but i want to fix it sooner than later so no more damage is done.

Any Ideas where i could start?

Thanks