Hello all! I am having some problems I was hoping you more experienced motor heads could help me with. I am new to the hobby but I am familiar with the terminology and the basic operation of the engine. Here is the problem:

OS .40 LA
Sig kadet LT-40
Average outside temp 90 deg
Low humidity
About 1500 ft. elevation

On the first flight of the day the engine runs well until the tank is about 1/3 full. At 1/3 full the Engine dies. On subsequent flights the engine runs rough and does not produce the same amount of power as the first flight. It is also more prone to die before I get to the 1/3 full state. The amount of power it produces is pretty much unacceptable. It barley pulls my LT-40 around the patch and makes go-arounds a little scary. Another thing is that is seems worse when I don’t allow it to cool off between flights. Oh yeah, also when I place my finger over the carb and turn the prop to prime it, I notice a wet squish sound that I don't remember hearing before. It may have been there and I just wasn't listening. Also, when I look at the fuel lines after the engine dies they are full of fuel, but there are small bubles in the line.

Here is what I have done (not much): First I used my pump to be sure that the fuel could be drawn all the way to empty, which it can. Then I changed the tubing inside and out side of the tank anyway.

Could it be over heating? Bad fuel? Carb problems?