It would be interesting to see what would happen if you added extra castor oil to your fuel. I usually top off a fresh gallon of store bought fuel with 6 to 8 ozs of castor. I have heard extremely good and extremely bad reports about the .75, after 2 years of struggling with this engine, even bench run problems, there must either be a random air leak or run away heat condition that causes the liner to grow out of control. Castor can solve both problems to a certain degree.