.. have you adjusted the mixture screw at all.. you could be so far off with the screws that it will not start or stay running..
The initial setting from Kohler are the following..
High Speed jet: turn the screw all the way in until it bottom out.. then turn back 1 1/4 turns
Do the same with the idle screw...
The adjust from there... first move the idle screw then the high speed...
You will notice the revs go up then down... you want the fine balance between them..
You will need the engine warm and reved to about 3000 to properly set the high speed jet..
Here is some good reading material for you...
http://members.aol.com/pullingtractor/carbfuel.htm