My thought is that increasing the carb would leave you where you are still at, maybe even worse off. Its like the big open funnel at the top, but you get to the restricted part where it all needs to come out, like the heads or even exhaust. Its only going to flow or pass the amount of air that is allowed through the heads and exhaust. If you go with a bigger carb you will probably lose the responsiveness that you have with the 600.