Roger, while it should have nothing to do with your stalling problem you might want to check to ensure both rear drivers are tight on their axles.
I've serviced many Berks and Turbines that were poor runners because one rear driver became loose on the axle. The wheel won't fall off because the flange rubs on the 3rd blind driver. In one direction the rear driver rubs on the frame, and in the other it rubs on the driver.
