Have a2008 Husquavarna riding mower, model 1538 lth,it stops running after 15minutes, like it is out of gas, before we replaced the engine coil it was doing the same, would restart after sitting for a few minutes, it seemed the hotter it got, the shorter it would run,it would take longer to start, that is why we thought it was the coil. The spark plug is throughly dry, looks great, should we assume the trouble is in the carburetor, any suggestions would be appreciated.