Call and talk to Larry Wolfe at jethangar.com. The old front carb K&B 7.5 ran, but poorly and was superceded by rear-rotor rear carb DF engines. The Turbax can be upgraded with a new center body from JHH to accomodate a difficult to find K&B 9101 or .48, an OS DF engine, or larger Rossi 65. But I would take Larry's advice and recommendation for the best powerplant for the yellow A4. You don't want to skimp on power and lose that plane on the 1st flight