ORIGINAL: mouthpiec
The engine is very difficlt to start (I use a chicken stick and the last time I tried it, a new glow plug was installed)
The idle usually is ok
On full rpm, once I find the appropriate rich/lean setting, is also ok
Transition from low to high revs is not always perfect.
The main problem of this engine is to start it, and that after a flight or 2, i need to set it again for optimum transition. (I am sure that the screws are not turning by vibrations, because I marked their position before the flight and the screws remained the same)
And what I meant when closing the carb intake, is that I close it with my finger, so I am sure that air is not going in, and still it takes too long to go off.
The fact that it is sometimes difficult to start, and then transition from low to high RPM are the primary indicators to focus on. When you say transition is not always perfect, I'm going to assume the engine hesitates when you throttle up, and then picks up to full throttle. Both the hard starting and the transition are indicative of an overly rich low speed mixture. These engines are sent from the factory with a rich low end setting. You are probably not dealing with an air leak, so I would not disassemble the engine yet.
Resetting the high speed needle after a flight or two is not uncommon, and is probably more due to the engine warming up, loosening up, and temperature/humidity changes that occur as the day progresses. Note that you do not set the high speed needle for transition. The high speed needle is set 200-500 rpm below peak RPM to the rich side. The low speed needle is adjusted for transition, and should only be adjusted in small (1/8 turn) increments at a time. After each low speed needle adjustment, the high speed needle should be readjusted before transition is checked. Once you get the low end set correctly, you shouldn't have to touch it again for the life of the engine.
As you get the low speed needle close to perfect, your starting will improve and your reliable idle will drop. I have two of these engines, and they both start with a quick back flip of the prop.
As for shutoff, make sure the throttle servo is adjusted to completely close the throttle with the trim switch or throttle cut, and make sure the throttle stop screw will allow the barrel to rotate fully closed.
These engines are designed to allow oil to flow to the front bearing along the crankshaft. The result is there will always be some air leakage in around the front bearing. If the throttle doesn't go fully closed, you'll never get the fuel shut off, and the engine will take a long time to cut off.