Freedom Z 26 horsepower briggs Cuts out.

the engine cuts off when 2-3 gallons have been used out of a full tank and choke is required to keep engine running with the blades disengaged
after 3-4 minutes the blades can be reengaged and resume cutting grass for approxiamtly 5 minutes then the problem occures again. I have cleaned gas lines and checked the pick up in tank. As long as tank is full,there is no problems. It has to run about 1-1.5 hrs ,then the problem starts. any solutions or info on this problem would help. Thanks Lewis in SC .

I would try two things. One try removing the gas cap, or at least make it very loose. Two, blow air into the tank with an air hose or your mouth. I know it sounds yucky. With the first test we want to know if the cap is not venting properly. With the second test we want to see if the fuel pump needs assistance.