silvertop = 43mm
blacktop = 45mm
thats at the butterfly, have sets of both here at home. Bike carbs are a good cheap way to get throttle response and reasonable power, economy can go out the window if your not onto the tuning. Great if your running a big cam as the pulses sent back up the inlet can interfere and give a real shit idle (which sounds cool ) seperate intakes = smooth as. The only way to get correct fueling for power, economy, driveability and to get it started first pop every time is with injection. Theres pros and cons both ways cost etc