I have experienced similar problems with a few other motors. If driving the car and being alot more aggressive on the throttle, the car did not stall, but slowly increasing throttle just killed the car mid way on the track. Try this. With the wheels off the ground, slowly increase rpm of the engine to the point where it is usually dying on the track. Hold the throttle at that point and see if the engine dies again. What I have found was the needle in the carb was at the point where it was just out of the metering tube, thus causing a high flow of fuel. I had adjusted the mid range needle to move the transition point where it wouldnt die as easily. I also found that using a different pipe helped.