RE: Engine tuning question
Engine reliability is 75% the user. The remaining 25% is the carb, engine condition, glow plug, fuel, head shims and some pure dumb luck.
The NT-16 that came in my CEN was okay. I had to adjust it about once a month. The OS I replaced it with, however, goes six to nine months between adjustments. All the mechanical factors combine with six years of experience have that thing purring like a kitten....a fat kitten, I'll admit, but purring none-the-less.
My protip is to settle on a tune slightly richer than perfect. Like, 1/8 turn richer on both needles. You'll prolong the engine life and put off the next carb adjustment.