Small Engines (Lawn Mowers, etc.): Craftsman Lawn Tractor Fuel

Question
Craftsman Model 917.273101 Garden Tractor:  22 HP Kohler twin-V.
The mower starts and runs only a few seconds before the carb runs dry.  I replaced the fuel pump and filter but the pump can't seem to keep up with the fuel demand. I also cleaned the carb, checked the fuel safety valve, float and needle valve and everything seems to be functioning properly.  I also checked the vacuum line and fuel lines and there are no cracks or leaks.

How much vacuum should the line be pulling? If I do not have enough, where else on the engine could I be loosing vacuum?

Answer
Do you have the Kohler Engine model #CV24S-75532?

If so, the URL below is the engine service manual:

http://www.kohlerengines.com/onlinecatalog/pdf/sm_24_690_07.pdf

Page 20 describes the vacuum check procedure.

If you loosen the fuel cap will the engine continue to run?

Let me know.
Eric