Okay, how can you tell if it's the air bleed type of carb? I am using a Zinger 18X6 prop, and the prop nut (barrel) bottoms out before the prop is properly clamped. The prop washer is there, as is the jam nut. As I understand from the instructions, there is an additional apacer (washer) available. Should I order this, or will the tru-turn spinner backplate that I will be using sufficient for this purpose? I have not yet ordered the spinner and backplate. I can work the prop issue out, but I would really like to know about the carb issue. I do not know how to tell the difference between the two types of carb. If I have the old style, would I be better off to order the new type carb? Thanks.