OK you blokes ! Here`s a little secret that I bet most people don`t know.
The first question you should ask yourselves is how much carby you can use ?
Most people don`t know the answer,they usually copy an existing set-up or take a ghess(like most on this forum).
EVERY engine has a maximum gas flow rate and an optimum carby size.There is a simple formula to calculate this !

Cubic capacity(in inches) multiplied by Max Revs,divided by 2.
This gives you the cubic inch of gas per minute it can breathe. Divide this by 1728 for cubic feet per minute (CFM).

For example: Lets say this comes out to 650cfm.If you fit a 750cfm carby,you won`t gain more power because the motor can`t breathe in any more ! But you WILL lose gas velocity & as a result droplets of fuel will form and tend to drown spark at lower revs.

Much better to err on the smaller side as, unless you get down to ridiculious levels, it is almost impossible to undercarb an engine.
You will lose top end power, but that`s about all.