ORIGINAL: Bolt_locker
If I set the high end needle to max rpm and then go 3 to 4 clicks richer, (200 to 300 rmp loss) and then set the low end for best transition and idle quality, the midrange is soooo rich that if you throttle back and after a few seconds throttle up, This engines ALWAYS burbles, stumbles and dies.
1) Has the engine been sent to the service center?
2) What is your fuel like? Fuel system?
3) A too-rich throttle-up usually means that the idle mixture it too rich. The proper way to set up the engine is to start out with a much too-rich idle mixture, get the full-throttle mixture adjusted so that the engine's running just rich of peak RPM at full throttle. Then throttle down to get the idle mixture adjusted. If it goes too rich on throttle-up, the idle mixture's too rich. You'll need to lean it a bit.
One thing to also consider is the idle RPM. Getting the lowest-possible idle RPM comes at the price of transition. You may have to give up some idle RPM to get a good transition. Any idle that's 2,300-2,500 RPM is OK. Lower is "gravy".