I really think it is in the carb. or backplate assembly. I don't have a floor in the cockpit and I am using the clear yellow tygon tubing for the fuel line. When it acts up, you can see the fuel draining back into the tank. Actual "large" air bubbles headed back to the tank just like if you were opening a petcock at the carb. If you choke the engine fully it will sometimes draw hard enough to pull the fuel back up and run very poorly ( can't advance the throttle or open the choke back up or it will die). I've taken it apart and cleaned everything spotlessly including turning the reed valve over the one time I dismantled and rebuild the engine and back again the second time with no difference. It still ran very well till it got warm (usually around 12 or so minutes) then sputtered, quit, and wouldn't restart till it cooled down. I've been able to restart it within a couple of hours after it quit. Something is warping or failing once it gets warm but returns once it cools down. The thing is that it used to run very well (just like when you first start it now) all the time. I really appreciate all the input!! Thanks again, Todd