GSX 400 carbs

[Disqualified]

Hi all... Just wondering if putting bigger carbs on can increase performance? standard carbs are 28mm

[F5 Dave]

Short answer, no.

. . .Well maybe faster fuel consumption.

New chain & sprockets would be a better bet. Stuffed ones chew power.

[geoffm]

Assuming this is for the Mighty Impulse...
In short, don't bother. The Impulse carbs are those mickey mouse Aisain twin throat things, and you won't get anything else to fit. I tried some CR Special smoothbores on my Impulse with a custom manifold but coudl never get it to work right, although it was ok on other ones.
Going to flat slides (Kiehen FCRs or similar) may give you more power - if they are set up right. You will have a more finicky bike, harder to ride (as they are not CV carbs) and it will be more affected by the weather and jetting. Bigger throats will total what little midrange the 400 has, and may not do anything unless the cams, ignition and exhaust all match.
If you have to ask, don't bother.
If you want more power, buy a different bike. A FZR400 makes 53hp in stock trim, and Impulse is 45 for a healthy one.
Geoff