Boy thinks again for all the information and post. I will get fuel with a mim. of 25% Castor oil. Will use a 10/6 prop because that's what I have at hand for break in. As for break-in procedure I will run sloppy rich (4 cycle) for an hr or so then start leaning out a little at a time if it sags I'll let cool down. I believe in compromise when there is a conflict of views. Since this is a RC engine it has a venturi with a very small carb. What a great hobby model planes are!