Patience, no PATIENCE, PAAATIENCE for .... sake (insert: the well-being of the engine and its owner, of course!) is essential.
Sometimes a little heat and/or a soft tap with a small hammer might help as well. After the soaking.
And try to understand first where exactly a little force should be applied and how - I think that most broken off handles of such engines are simple due to the fact they come so handy....
Nice engines!