The problem with a go kart not steering is the center of gravity. One of the things you can do to find out (from a diagnostic standpoint) what is up with the steering is to weigh he go kart.
To weigh the go kart get a scale and place it under the rear wheels and then under the front wheels. (The scale can be placed under the framework but in line with the wheels.)
Make sure that you the rider are on the go kart when you measure the weight. (Have someone help you to read the scales.) It also might not hurt to have multiple people sit on the go kart to get an average weight.
The two weights together will give you the full weight of the go kart. The weights should be very close.
More than likely the problem with that go kart is that too much weight is on the rear wheels. When this occurs, then the front wheels do not have enough weight ( or grab) and allow the go kart to continue forward.
Additionally, the problem may be that the engine weight is too far back on the frame and may be causing a balance problem. (Or cause the go kart go be in a wheely type situation)
I became digusted with the unsteerableness of gokarts and designed my own so that the weight was more balanced.
The key is to get the wieght over the front wheels too. Look on the Engineering Tool Kit Section and the Center of Gravity program.
You may want to put your go kart data in this program and see what it says.