I don't think they make adjustable carbs for the OHH motors. The ones for the H and HS engines are adjustable, but I think the throttle works backwards. If I have time this evening I'll check it out if I can find My old OHH carb. I'm going to put a 19mm slide carb on mine. I'm pretty sure I read somewhere about the throttle working opposite. There is a chance you could swap out the throttle shaft and butterfly if the carb bore was the same size.