The engine is not a race marine engine. It is for a sport nitro marine engine, HB 61PDP I am putting in a boat for another teenager in my neighborhood. I have built 2 so far for that. I rebuilt the motor, piston, ring, bearings, and gaskets. I want something that will add a little more to the performance to the motor. It didnot come with a carb as I got it used. Anyway, most of the high performance 21s, ie, nova rossi, rossi, cmb, and others with the slide valve carb 8mm will work. Their carb opening in the motor is for a .530 or 13.75mm. Don't know of others specifically. I have a nova rossi 21 and tried mine, it fit perfectly.
Curt