This is an indication that the low-speed mixture is too lean. Suggest you enrichen the low-speed mixture adjustment 1/32 of a turn at a time until it will accelerate without hesitation or dying altogether when advancing the throttle rapidly (approx. 1-2 seconds from closed to full open). Notice this is rapidly advancing the throttle, not "snapping" it open or immediate full throttle. Snapping it open is a technique to avoid as it momentarily starves the engine of fuel, causing it to hesitate or quit. Once you have the low end adjusted, readjust the high end as the low end adjustment will slightly change the high end as well. I like to set the high end on the rich side of the peak RPM using a tachometer. In other words, find the max. RPM and then enrichen it just enough to drop the RPM approx. 50-100 RPM off the peak. Hope this helps; let me know if you're still having problems and we'll go from there.
Great job on the new website! Thanks for all your work on it.