id say yes that would probably give you some good speed.
A 115CC engine is fast for a go-kart. It should enable the driver to get some good speed. You can also use a 110CC engine.
There is no direct conversion between cubic centimeters (cc) and inches, as cc is a measure of volume while inches is a measure of length. You would need to know the specific dimensions of an object to convert cc to inches.
16ounces =454gm approx454 /125 = 4.4 oz approx125 grams is 4.41 ounces.About 4 1/2 (28.3 grams to an ounce)