I was asking my guy who built my Olds motor about what size carb to use and he said most guys get them wrong because jets love CFM's but not all that fuel so he uses large size carb and cut down the fuel circuit side some and my carb seems to be right on the money. I have great performance and good mileage for what it is as long as I keep my foot out of it somewhat and I do not know the size of it but it's double feed with mechanical sec and I think it is an 850 with smaller jets with an wooden spacer between it and the manifold.