Tune the low end while the engine is idling. Use a small flat blade screwdriver and slowly turn the idle screw in while listening for a rise in rpm. Stop when the rpm stops rising and then richen the low end just a tad. Let the engine idle for around 20 seconds. If the rpm slowly sags and the engine stops, then the low end is still too rich. On the other hand, if the rpm slowly increases and the engine stops, then the low end is too lean. Also, if you jam the throttle stick forward from idle and the engine stops, then the low end is too lean. Adjust and check again.