the carburettor has been bored out to 33mm, this is the maximum you can go to without weakening the casting, theres a whole lot of work in the carb, the baffle shoulder needs shaping to give a good air flow, the fuel passages need massaging and the cross drillings need to be worked, the carb is very primitive but the regs state that this is what you have to use, shame really, a nice big hsr 42mm mikuni would give loads more power.