It seems to run better or longer on a full tank of gas before it starts acting up,
First of all it sounds like a gas tank vent issue, BUT the above quote leads me away from that as it usually runs longer with less gas becasue there is more air to remove b4 it starts acting up, BUT lets start at the tank vent becasue it is easy to test.
TEST: With less than a full tank just remove the gas cap and run without it, (less than a full tank becasue a full tank will bounce out gas
) does it run past 30 mins now? If yes replace the cap or the vent line.
Next, there is a pickup tube that is in the tank and pulls fuel, it can be caught on somehing inside of the tank or if old enough, the ethanol can cause the rubber pickup to curve up, so when the tank gets low, it cannot reach the gas even though there is some fuel still in there.
Cannot speak to your specific model but you need to get to the tank and check the pickup tube...
Carb issues are another possibility but lets start with the easy things first! (not that a carb cleaning is hard, but if you are going to do a carb cleaning replacing all the fuel lines is suggested too, and the PROPER fuel filter is important, even if they look the same they can prevent flow)
Please post back, we can help you get it right!