Went out to the flying field today. The engine started up easy enough. I made a few adjustments to get good top speed and set the idle speed with the radio and off I went. It ran good, one fellow made a comment about more power ( a .58 on a .40 trainer takes off rather quickly). I made several laps and I was just about to think my problems were over then on about a quarter throttle it stalled. I landed without any problems. Upon restart I could not get the engine to pay attention. It would snap to life, rev like mad at top end then return to a slow steady idle. I would taxi onto the field, wait my turn then advance the throttle and it would stall instantly. I did this 5 or 6 times making adjustments in between to no avail. I hate to badmouth, but I am not having any luck with this engine. This is the second one I have had and it does the same thing. I am just about ready to sh**can this motor. I really dont know what to do next.