I'm rebuilding a gsxr400 73 sp at the moment, and can't wait to get it on it's ear round a track.
But... I've had a real time just trying to get it to run smooth, and sussed out it was a air leak between carb rubbers and cylinder head. I could not even balance the carbs, the adjustments I made were confusing according to the gauges.
I'm using 73a sp/bandit 400 rubbers (13110 32c10). I've rtv'd them at the moment but might machine them if I can find a suitable way. After 25 years I think the rubber shrinks away from the metal backing, and even thought they look mint to the naked eye, could be troublesome on bikes that haven't run for ages.
Nick.

Are these available new? If so i'd just change them next time the carbs are off?

There are differences between the models,
Some bandit ones are about 10mm longer and have a o'ring between the rubber manifold and the head, you could machine the gsxr one to accept an o'ring stopping this problem.
The non sp gsxr has an ally spacer between the manifold and the head that makes the inlet track longer, the sp has no spacer, just the manifold so different air box to offset this.

Hi, Yes they are new £25 each from Suzuki.
Good idea on the orings. The 13110 32c10 rubbers are used on the bandit 400 as well as the 73 sp. The bandit has an additional alloy spacer which does have an o ring which the 32c10 rubbers mount onto.
Most Suzuki carb rubbers have the part number labelled on them for easy recognition.
Nick.